Main options are Devil’s Drink fight club(feed the hungry hobo at the camp a few times and he’ll clue you in), once your magic is good enough you can easily make 4k a loop, give or take what you spend recouping magic and lust
Stripping, which scales infinitely off your Ero and doesn’t have a repetition limit per sleep cycle, plus it only needs stamina
A slower but real option is dumping 100 milk into the refinery at the farm(buy it in Upper New Ark’s Mall) and coming back later, it sells for 20 a piece
Technically you can be more efficient by turning it into cheese slices(5x5), but you can’t mass-produce slices in one action, unlike the Potion+ items so thats tedious and unhelpful