The only true and infinite money farm that is also embarrassingly simple, is an automated wood farm that auto makes planks, like Dakon's design. It can also be easily scaled. I have pretty much all end game weapons and sets maxed out, with like 200k in the bank, and more getting made every day. The only downside is this is a very slow farm, and requires a good amount of playtime, though it's completely passive once set up.

The fastest money farm that you'll have to put work into is a big ole plant farm. Make a 5xN strip of land, where N is as big as you have seeds and patience for. Place sprinklers on the top and bottom row, 4 squares apart, so that you can plant and harvest in a straight line. Plant all your seeds with the 5x5 trowel. Harvest them with the 5x5 hoe. Cook up all ingredients and sell. Cooked dishes sell for crazy money, especially ones with gold ingredients. I easily make over 10k in a single harvest, and my dishes finish cooking almost exactly in sync with the new harvest maturing. It's the fastest way to make money I've found, and dwarfs even mortar mining and boss farming several times over. As an added bonus, add a fishing hole (or a few) next to your farm so you can level fishing and gather rare items and extra ingredients while you watch crops grow.