On my chill save, in Spring Y3, I'm at 2 million every Friday (primarily from the changing over of the kegs). The last shed I built and filled put me over that mark. I know on my longest running save on the standard farm I was up to 5 mil per week during non-winter months, but even then I don't think I ever saved up stuff to sell all at once, so my per day figure was unlikely to have been substantially higher than the 2 million mark.
My biggest loss depends on how you look at it. Either, it was the (pre-1.4) purchase of 20 stacks of Stone for Staircases, which was a recurring expense and each time set me back a cool 2.4 Million, or it was when I was KO'd DEEP into a SC run and it showed my Prismatic Shard collection, which at the time I'd just been carrying around on me and was over 600, as being "lost". The Stone I at least was getting something back for the money. The Prismatic Shards, that was over a million in value just Gone (no item recovery service at the time). However the Shards, I immediately "NOPE"'d right out of the day and quit the game, so I didn't end up losing them. Either way, it's definitely in the mines in which I've sunk the most money, no matter how you look at it.