My current game has about 35 money trees, always kept fertilized with Life Fruit. The daily harvest is about $20-25,000.
I've found that cherries make outstanding fertilizer too, with minimum maintenance, so my garden is Money Trees, Life Fruit, Cherry Trees, and all varieties of Perfect nectar grapes. I'm saving up the grape harvests in a chest to be ready for nectar making.
By the way, once you can grow steaks, the high quality ones sell for a lot at the consignment store.
Edit: corrected daily harvest amount