I'm in the same situation I have mine sitting in my garage with all the rest of my junk. If I were to sell mine I'd probably look for $30-40 a piece.
Dunno if it's considered fair or not but anything more then that and probably not a whole lot of people would be interested and anything less than that I'd just rather give them to little kids to run around and pretend like they are shooting stuff

Edit: looks like you can buy brand new ones for around $70+tax so I still think $30-40 should be reasonable if they are in good condition.