Here you can see how you can get the most and easy money.
How to Farm Money (Easy Method)
How to Make Money Fast?
Farm green gemes in mine and make upgrade them at the gem craftinstation and sell these.
I recommend only farming those green gems, cause aquamarin and topas only drop in lower density and are guarded by stronger and much more annoying enemys.
I get 5-8k every day with this. (Best thing you can do early on for money).
As you level your mining skill you get also more gems from these gems in lower floors. and even later from second and third dungeon than.
I recommend selling the gem of the lowest floor where you get 8 gems per harvest. (more difficult gems will get you 1-3 which isnt efficient.
Also I recommend you to buy in the second biom unvisible potion (60gold) so that you can mining without fighting monsters!