Might be worth looking at something like Curtis Fitch to see if their isourcing software can help - apparently you can set it to do a variety of auction types - reverse auctions etc. Our purchasing department use it to source suppliers and also sell stuff for clients when they have excess stock.
Might save you reinventing the wheel for the tech side, leaving you free to focus on your business side.
http://www.curtisfitch.com Good luck mate!