Take a trip to Vegas and go visit the Pawn Stars guys... tell 'em you wanna sell it, and they call in their expert who values it for you, then let the pawnshop guys lawball you, disagree and walk out. Not sure about this but you might get paid for doing the TV spot.
There you go. Free valuation by an expert, and you get to go to vegas too. :D
Bonus - if Greg wants to sell it, everyone who watched the show knows that he has one for sale and all he needs to say on his online ad was "featured on Pawn Stars". :D :D :D