Thanks for the comment, FlamingFoxu~! Are you getting most of your money from Arena fights that use Aggression? I find that the Arena is helpful in the very early game, but doesn't give very good profits long-term. I think the best way to make lots of money is to train girls in the School so that you can sell them. After I make my first or second girl sale, I generally have enough money that I can just ignore the Arena.
Ah, I see~ After you play a bit more, let me know if you still find it too difficult. One tip I posted on my Patreon page is that lowering the number of races available makes the game much easier, because it's easier to match the requests of Wanted Ads that ask for a specific race. I normally play with 8 or 9 races rather than all 14.