Jeez guys, cut him some slack. He can price items however he so wishes - whether it's a value that he himself finds agreeable or one that you find unreasonable. The arguments are becoming redundant. Even if he was charging 3 euros for this Wertham release, I doubt you'd be coming to his rescue and saying "hold on buddy, you could easily get 30 euros for that!", would you? No, you'd probably snap it up immediately and keep your mouth shut. But I don't really want to see another discussion starting about 'reverse opportunism' or some other such nonsense...
Hope you get a sale for your items to decent and understanding collectors who appreciates the artefacts for reasons beyond the price paid for them.