True Polymorph is the easiest if we just wanna accrue wealth quickly

Buy some live feeder mice (a small animal that doesn't involve killing someone's pet) and transform them into jewelry. True Polymorph has none of the restrictions of Fabricate, so we can create fine jewelry without skill. Turn a mouse into a gold ring or necklace, with a large gemstone embedded into it. Sell it at a pawn shop. Repeat, use different pawn shops, and use Dominate Person with Modify Memory afterwards if theres some law about needing an ID. The dominated person can use theirs, and then you remove the interaction from their memories.

Sell fine jewelry made from mice all you want. Use that cash to buy cows or other massive animals, turn them into gold. We don't have to worry about how to pass the gold off though, the goal was to accumulate wealth. Use Fabricate to make the cow-gold into rough coins, build a secret dragon's den.

Of course, if we're willing to be a little less subtle, True Polymorph is also great for doing some light faith healing, restoring blindness due to injury by transforming them into another person that's basically identical, or we could make people look like their ideal selves. Not in the bounds of the question though.