Listing on eBay used to be my job and while it isn't so much anymore, I still do list a good deal of items and am forced to use Paypal (it is not applicable in this situation, but you would fine an actual merchant account isn't so great at preventing buyer fraud either.) There are other options than eBay, although it is the most visited and popular by a ridiculous -and arguably disappointing - margin. You could try use different auction sites, or online classified sties or rely on Cheap Ass Gamer forums. In the trading forum many people do deal with cash or money orders only, so it can be done.
The Postmaster General isn't likely to help but I know from personal experience they will sometimes help in cases with relatively small amounts; it is a crapshoot really. Now threatening the buyer, whether you intend to follow up on it or not, is the option of last resort. Only do this if you think there is absolutely no other option - I have found speaking to the buyer on the phone can sometimes have positive effect, so you could attempt to call him and negotiate a resolution before dropping the fraud bomb. All in all, you will be required to sacrifice something, whether it be money, merchandise or simply your time.