Back To The Future II's hoverboard just sold for $501K, which is pretty steep since it doesn't actually fly
The prop hoverboard was signed by both Michael J. Fox and Thomas F. Wilson

Back in September, we learned that a whole bunch of famous movie props were about to go up for auction this fall. Now, that auction has concluded and, as part of it, some poor rube spent more than half a million dollars on Marty McFly’s hoverboard from Back To The Future II, presumably not knowing that it doesn’t actually fly.
Despite the fact that hoverboards not only exist, but have been available to ride in their faux-future form in the past for far more realistic prices, Smithsonian Magazine tells us that someone with more money than sense spent $501,200 for a prop version of one that just lies on the ground uselessly.
This specific Mattel hoverscooter-turned-hoverboard may be incapable of helping its new owner escape gangs of sneering bullies, but it was signed by Michael J. Fox and Biff himself, Thomas F. Wilson.