Casual Players wanting more paths to be viable or to feel less harshly "punished" for not picking the optimal "meta" choices, Experienced Players seeking to extend the mid-game before they are able to easily buy all the end-game items, Min-Maxers who want more variety among the optimal choices depending on circumstances, or Longtime Players looking to re-experience the process of trying out a variety of unknown choices and working out which ones work best with their playstyle on their own.

Goals of this mod:

Using spreadsheets simulating a variety of scenarios and carefully adjusting the prices of most crops, seeds, animal products, animals, and a few other details while changing as little as possible to maximize compatibility, this mod aims to:

Further Reading:

The points above summarize all the big picture things this mod should accomplish.  The specific changes vs. Vanilla can be seen in the Price Changes article.  Check out the "Individual Overviews" article for charts showcasing the strengths & weaknesses of crops in typical scenarios, and brief written overviews for special cases & animals.  Or don't, if you want to keep it a surprise and recreate the "blind first playthrough" experience of working out which things work better in certain situations on your own.  The "Explanation & Background" article is if you want to dive into some of the assumptions made while balancing, or the thinking behind the "how & why" for much of the changes. 
Be aware that the various articles may have unmarked references to some 1.5 content if you are avoiding spoilers, but all 1.6 spoilers are in a spoiler container at the bottom of "Individual Overviews".  If you're especially curious, you can look through the spreadsheets I used for balancing the various aspects in the Miscellaneous Files section, which also shows the profit for various configurations of both modded or Vanilla items.  The crops sheets in particular are based on a modified version of the wonderful Stardew Valley Community Spreadsheet's Crop Income page, with various corrections and additions.  The Recommended Mods & Optional Plugins section below is also highly recommended, optionally.

• Install the latest version of SMAPI
  

• Install the latest version of Content Patcher
  

• (Optional) Install the latest version of Generic Mod Config Menu
  

• Download the zipped file, and unzip its full contents into your Stardew Valley\Mods\ folder.
  

This mod should work as expected with the Vanilla "Profit Margin" settings, although doing so will affect the balance of/between items.
That's all you need to start using it, although there are some Recommended Mods & Optional Plugins detailed in a section below.

Please note while this mod should work without any issues on an existing save file (see paragraph below), the full effects of the balancing changes will be most noticeable on a new save file.  I believe this mod shouldn't affect the save file, and should be safe to uninstall at any point.

For using with existing saves, note that while all newly generated/harvested items should have their prices adjusted accordingly, any existing items that are already in the player's inventory, or in chests, or have already been spawned by machines, animals, or on the ground as foragable items on the dawn of the in-game day you install this mod will still have the old Vanilla prices.  To fix existing items with old prices, put them in a chest and then bring a stack of 1 or more matching items with the correct new price, then pull the old items out of the chest so that they join the new items in the player's inventory, where they will convert to the new price.

If using the Generic Mod Config Menu mod to change the price of items mid-day by changing the setting from in-game, the same process above applies.

Customization:

The values in this mod are the result of many hours spent simulating the performance of different options, but all of this has been done according to my personal tastes for balance.  Users can easily make any price adjustments by editing .json files in the Better Balance\[CP] Better Balance\assets folder, which should have names & descriptions for the changes commented behind "//". In particular, pricesBalanced.json contains the vast majority of all price changes, with changes specific to the Stardew Valley Expanded mod in SVEPatch.json.

There are also 2 config.json files, one in each of the "[CP] Better Balance" and "Better Balance" folders. 
The descriptions for the effects of the different settings can be read in content.json in the Better Balance\[CP] Better Balance folder, or read in-game if using the "Generic Mod Config Menu" mod. Toggling some of the options mid-day can require reloading the save / sleeping through the night to take effect.

Aside from the various settings to disable individual adjustments, the config includes values to apply price multipliers to all items within certain categories: Fish, Animal Products, Animal Resale, Crops, Farm Forage, Flowers & Honey, and Cooked Foods. This allows you to broadly adjust the balance between different playstyles/aspects of the game quickly, without having to go adjust each item's price individually. Changing the prices mid-day with GMCM can still adjust pre-existing items by following the steps above in the "using with existing saves" section. Note that changing these multipliers will affect the profitability & balancing of all items within that category.

Compatibility:

As a relatively simple Content Patcher mod with few C# functions, this mod should be fairly compatible with other mods, so long as they don't also specifically attempt to alter the prices of the same crops / seeds / animal products in Data/Objects, or the same animal prices / production times in Data/FarmAnimals, Data/Machines, or Data/Shops.  (For example, SVE's custom "Lower Profit Margins," or Longevity's "Price Balancing" settings overwrites many of Better Balance's changes) Mods which change other things in those files should probably be fine, as far as I'm aware.  This mod also dynamically alters the prices of several items in some shops, so other mods which attempt to change those same items may run into issues.

Though all the mods in the Recommended Mods & Optional Plugins section seem to work fine together with this mod for me, they may have their own compatibility concerns to check if you're using them alongside other mods. 

Using this mod alongside mods which add new crops or animals should not cause any errors, however note that this mod only rebalances the Vanilla (& most Stardew Valley Expanded) crops & animals, so any mod-added items will likely be more profitable than the Vanilla items.  Thus to gain the full effect of this mod I recommend either using it without any modded crops / animals, or only using modded crops / animals sparingly to avoid becoming too overpowered. 

Recommended Mods & Optional Plugins:

Optional Plugins for further Balancing:

Stardew Valley Expanded
(or the standalone Crafting & Construction from SVE mod)
NOTE: Currently, enabling SVE's custom "Lower Profit Margins" option in the config overwrites many of Better Balance's price changes, so using both together is not recommended.

You've likely either already heard of Stardew Valley Expanded (SVE), or are currently using it, although I'd recommend giving it a look if you haven't.

Related to this mod, however, are the "Balanced Crafting" and "Harder Building Construction" options in its config.  Together, these generally make many useful items & buildings require more resources and/or money to craft or build, with special attention to many high-performance items like Kegs or Iridium Sprinklers requiring more.  However, some underperforming items like default Sprinklers have cheaper recipes to encourage their use in exchange.  Overall this goes a long way to solving the "exponential snowball" of Year 1, and I appreciate how many repeating recipes requiring both more Wood and Hardwood make the Lumberjack profession more appealing.  The increased costs & recipes feel fair, as if correcting oversights, rather than introducing tedium for the sake of it.
The full changes of these two options can be compared with Vanilla at the SVE wiki pages for Balanced Crafting and for Harder Building Construction (wiki may not be updated for 1.6 yet).

I always play with SVE & these settings enabled, and so while you can certainly use this mod by itself, your experience will be closer to how I've tested it if you use them.  

If you are using SVE, by default Better Balance will adjust the price & value of SVE crops, and the price bonuses you receive from various NPC events to be more in line with prices in Better Balance.  You can see the exact changes to the bonuses at the bottom of the readme document. Aside from these, while SVE tends to offer more numerous & valuable gifts or opportunities than in Vanilla, such as free Strawberry Seeds in the mail early on, profitable fishing spots, or shops offering rare items, generally these are marked by coming from SVE NPCs or being in special SVE areas, which makes it possible to avoid using them if desired.

However if you don't use SVE, with permission I have supplied the standalone mod Crafting and Construction from SVE which just duplicates the effects of the "Balanced Crafting" and/or "Harder Building Construction" options from SVE.

Predictable Retaining Soil
Makes the water-retaining soil fertilizers have a set number of days you won't need to water the tile, instead of being chance-based. A simple change that opens up some interesting new options as it makes these items actually potentially worth using (In vanilla since you'd need to walk around to all the spots that dried out and water them individually, these soil fertilizers wouldn't actually save you any effort). Can configure the amount of days watering isn't needed, e.g. I use 1 day for Basic and 2 days for Quality Retaining Soil, since rain will reset the timer.

Ease of use:

Generic Mod Config Menu
Makes reading the descriptions of the special config settings & Multipliers easier, and allows adjusting them all from in-game.

Lookup Anything & CJB Show Item Sell Price
Very handy even without any other mods, being able to see the value of items in your inventory by hovering, or check the stats of a crop / animal at the press of a button is extra useful with this mod as many of those values are different from what you may be used to. 

Notably, using Lookup Anything on seed packets (even in Pierre's inventory) will allow you to click on the name of the crop itself and see the stats for it without needing the crop itself in your inventory.  Synergizes well with Price Fluctuation to see the predicted value for crops by checking the seeds in Pierre's inventory.


Variety / Challenge:

Leveling Adjustments
This allows you to set your general experience factor to something like 0.5, to make you gain all skill experience 50% as quickly, which can really help extend the early/mid-game before you unlock all the powerful recipes & abilities. It also makes the choice of what activities to do in the first few days and weeks feel more impactful, as you may have to focus on a particular skill to reach a certain breakpoint you would normally, e.g. getting +1 Forage Berries in time for Salmonberry season. With the way the experience requirements for levelup are set, setting an experience factor of 0.5 would make you be about 1~2 levels below what you would be in a vanilla game, on average. While this mod is not technically updated for 1.6 yet, there is an unofficial update posted on the mod's Posts page.

Enhanced Relationships
This can indirectly slow down gaining friendship/hearts with village NPCs. Note that currently by default it will actually increase friendship with affected NPCs, but if you set both "BasicAmount" and "BirthdayMultiplier" in config.json to negative numbers it will slightly reduce your friendship with each NPC every day unless you've already given them a gift that week, scaling down based on how many hearts you have with them already (with the default values each day you lose roughly half the amount of friendship gained by speaking to someone, and more if missing their birthday).

RTGOAT's Longevity
(Now updated for 1.6 and more compatible with Better Balance!)
Longevity falls under the "added challenge" category, though I still wouldn't consider it to be unfairly punishing or grindy, and personally always use it.  One of the oldest and best mods aimed specifically at improving balance / extending the life of the game, which I always play with, much like SVE.  Specifically for using alongside this mod, I especially recommend using the Taxes and Stamina Balance features, although the Diminishing Returns and/or Random & Seasonal Fluctuations under the Dynamic Pricing feature (which may "unbalance" some prices in certain ways) can also add some interesting strategic choices on when to sell things or planting an unexpected crop because the seeds were on sale.

Taxes will give a set amount needed to pay each month (increasing with the number of buildings, sprinklers, machines, etc. on your farm) as well as a small percentage of your income, starting low and slowly increasing akin to a progressive tax scheme.  This helps by not only providing a "gold sink," but the progressive tax scheme means that it becomes more noticeable the "better" you are doing, and less of an impact if you are playing more relaxed / just starting out, so it never feels overly punishing just for the sake of it.
Stamina Balance gives slight tweaks & increases to stamina consumption for the various tools, which also helps curtail the "snowballing" of Year 1 by reducing your effective energy, and also scale with your tool upgrade level to still be relevant even later in the game when energy is easier to restore. 

Longevity's Dynamic Pricing is now compatible with Better Balance as it works as % increases or reductions to the base values in the game files, which Better Balance adjusts directly, so any of the Influence numbers you set in its config (if done through the Generic Mod Config Menu it includes helpful descriptions) work as % multipliers that stack multiplicatively with any Multipliers you set in Better Balance's config. In particular, hopefully Better Balance makes most crops competitive enough with each other that the daily Random Fluctuations feature (even if set to just 10% variation) should be enough to possibly change which seeds you buy at the start of the season, based on if any happen to be on good discount that day. If you only want to use one or two of the Dynamic Pricing features, such as the Diminishing Returns based on the amount of the same item you've sold recently, or the daily Random Fluctuations, you can just adjust all the other Influence values to 0.
Note that if Dynamic Pricing is enabled, Diminishing Returns will also always be enabled which will incentivize producing high-value, low-quantity items, and fruit from Fruit Trees (or jellies / wines made from them) get "negative" diminishing returns, where they instead increase in value the more of them you've sold recently, potentially making them overly profitable.

Special Thanks:

This mod began as a personal project to just rebalance a few of the more egregious things in my own game, but eventually sprawled to balance so many things that I figured I'd offer it for any other users who happen to share my same tastes for game balance, or as a tool for others to do the same on their own.  Especially since I've already relied so much on the efforts & information provided by the Stardew Valley community and modders when playing over the years. 

Big thanks in particular to:

ConcernedApe, for making a game that has brought so many people together.

Pathoschild for creating the framework for someone like me to make a mod in the first place with Content Patcher, and all the other incredibly useful mods & tools they've made.

FlashShifter for all the work on Stardew Valley Expanded in general, and making the standalone version of Crafting & Construction from SVE available in particular.

Digus for the work on Custom Crystalarium Mod, and especially making it so easy to create content packs for it.

Modders such as lech43 and RTGOAT for creating balance / challenge oriented mods, despite the game's relaxing reputation.

The entire Stardew Valley modding, Discord, theorycrafting, and playing community for making so much information such as the wiki or community spreadsheets available to players and creators.