If you're so worried about losing money, then why not just spend it all? Besides, if you lose to the last one, then you've gained money from defeated the first few of them anyway. You'll never go bankrupt, and you'll still get exp. Rather than switching your DS off and lose the exp you gained by defeating at least some of them, just do your best. And if you lose, just accept it and try again. You'll gain exp, and also gain cash rather than lose it. It's a tried and true cycle of events.
EDIT: By the way, the amount of money you lose for losing a battle is determined by how much you had before you entered the battle. You lose 50% of your money if you lose a battle. (Decimal places are rounded down.) There's no fixed amount. So, you can't say that if you lose, you lose a lot of money. That's only true if you had a lot of money to begin with. As such, if you had P10, then you'd lose only P5 if you lose a battle.