DAm 6 weapons at difficulty 10, I can hardly make any money thanks to the high hp monsters that scale way too much per difficulty. (MAKE it get money from the damage please)
Gaa I tried my 4 minute super fast pace song at difficulty 8 and the whole screen was full of monsters with so much hp. It was hard to kill anything and it felt like a bullet hell game. I had to watch out for nearby monsters shooting point blank shots at me (throughout the song). I died.
TO farm when you have no weapons but some shield (get 3 for best), go to lvl 25 and just move directly up so the high money yielding ships crash into you thus taking their gold (you got slight invulnerability time after getting hit but the so you can crash into multiple ships with 1 shield). You can get 180 gold in like 5 seconds.