You could try posting it in the Classifieds section of this forum (scroll down a ways on the main forum page and you'll see it). I've always sold guns either to a dealer or private face to face deals. I've bought a couple guns through Gunbroker, and there is no fee to buyers, but i'd imaging there is a sellers fee as usual for auction sites, but I don't know what it is. Try the classifieds forum, maybe you'll find a buyer that's close enough to do a f-2-f transaction even if you both have to drive a little to meet in the middle.
Mike