I've used paypal gift without any charges in the past for small transactions.
If you keep the money within paypal - ie. anything you get in, you use paypal to spend again, rather than withdrawing to your your bank account - you shouldn't have to pay anything.
However, you don't get any protection against fraud, and if you do it too much you could get suspended for trading....having said that, I did a group buy for another forum a year ago with it and didn't have any problems. (thankless and hard work though, not recommended...)