The two main ways of making money is
-> do government board hunts and defeat bandits/thieves (Slow and enemies scale with you so it takes relatively equal time regardless of your power)

-> make wine


Honey Peach Wine: Deer Antler(50) + Advance(Aggressive) Glutinous Rice (50) + Honey Peach (120)

each combo costs around 220 gold for the materials (50 + 50+ 120)
you get around 4 wine/craft
each wine sells for 1000
so you are making (4000 - 220) = 3780 profit

An hour of this can easily get you 300k which is enough to buy all the items from the black merchant

The main thing to do with money is to upgrade your weapon forging skill by mass forging level 4 and level 6 weapons.
This is so you can eventually get level 9 and craft the BiS weapons.