Infinite Gold, Infinite Nether Katal Materials.
For infinite Money you need Only a few gold (1000 at least) and some patience.
If you have a Nether Katal like "summon rat" or "Fear", just go to a Magic shop that sell material for katal (the witch into the Devil's March fit aswell, and she sell some katal, if you need some).
you could can see that the materials are quite cheap (like for fear, 10 gold + 10 gold) but if you mix it and just resell it, it would be something like 700 Gold.
So you turn 20 gold in 700 gold, and that is no cheat, just ... work.
Do it until you have the gold needed, quite simple but maybe a little long.
If you want to use rare or complex Katals that require unusual materials, just sell one of these materials, and buy it back, but 10 of them. You have to pay for it but the "rare" material is now sold at your material shop (works fine on Soulstone, Mandragora, Homonculus, ....all).