Well, it is a difficult question.... I think the above post is right. As a 12.6 gun, its value is going to be fairly modest. Anybody with a 12.6 can pick up all kinds of little PPK-type guns of all descriptions very cheap, and has been able to do so for... well.... 13 years.
But for the rest of us without 12.6, it's a whole other ballgame. As a restricted firearm... it could be worth at least a couple hundred more. Depending on the level of interest, it could be even more. The problem is, it would probably cost at least a couple hundred (probably more) to have it converted to restricted - so guys like myself that might buy it to convert it are only going to want to pay $600 or so.
If you do have one, I'm interested. I'd have to transfer it to Joe Dlask and have him re-do it for me... but I'm interested, and I think a couple more guys are as well.