Sending cash is really your best bet.
I went through a big phase of selling all my old RPG stuff on ebay when I was a bit strapped for cash (I still can't believe how much the compleat book of ninja's went for) and the cheapest thing to do is send the notes. You could send dollars which the seller can then use to buy stuff from americans, or Euros which you could get at any travel agent really for not too much of a commision.
Don't send checks, I used to hate it when americans sent checks!
(edited when I remembered the Germans don't use marks anymore)