Everyone’s advice is spot on and should really help you out. For short term cash, I do have an idea. Well, I wish I could claim credit for this.
So, my advice is tea tree saplings. Wickedy Chickedy released a YouTube video on this strategy, if you need more detailed information than I can provide you. She made over 1,000,000g her first year selling tea saplings alone.
First, befriend Caroline. If you talk to her every day and give her 2 gold star veggies a week, it will only take you 14 days to get her to 2 hearts. 2 hearts is all you need. I didn’t talk to her every day and gave some normal veggies as gifts. I still managed to befriend her in 16 days.
While you earn Caroline’s friendship, gather and hoard all of the wood and fiber you can. Also, forage as many horseradish’s, daffodils, dandelions and leeks as possible, turn them into wild seeds, plant them, harvest them and repeat.
Once you have 2 hearts with Caroline, enter the room in the back of her kitchen. If a cut scene doesn’t trigger, try again on another day. Once you’ve seen the pretty awesome cut scene (you’ll never look at Caroline the same again), she will send you a recipe for tree saplings in the mail.
You need fiber, wood, and wild seeds to make tea saplings, but they sell for 500g each. Just 20 of them will net 10,000g at no cost to you. As a bonus, you will be doing a lot of wood cutting, fiber harvesting and foraging anyway, so this strategy won’t really interfere with your other activities.
Good luck!