There's a Neo Geo game called Aero Fighters 3. Until this month, it was assumed that it had never been released in the US. It never was, officially. But at least three copies are now known to exist anyway, and one of them just went for over $30,000.
Reader Michael DiCioccio, a hardcore Neo Geo collector, says that he found out about the copies of the American edition of the game - of which there were only three ever made, presumably as testers/demos and never publicly released - from an ex-SNK USA employee, and that they've been sitting in storage for 16 years. He got hold of two (that's it pictured above), had them verified as authentic and sold one for at least $30,000. At an airport. Hopefully in an aluminium briefcase, wearing a trench coat.
Neo Geo games were expensive enough when they were new at retail. They're no slouch now, and for a game as rare as this, $30,000 (or the ballpark, Michael understandably is reluctant to reveal the exact tally) seems almost a steal.