Do you guys accept steam cash? I don't have a credit card so there's no way of me paying you guys. :/
Options:
Set up your bank account to work with Paypal. This will take a few weeks.
Get one of those prepaid credit cards. You may have to wait about 10 minutes after registering it, then it should work through paypal.
Buy a game for someone in exchange for them paying for your RTB service.