These things are funny. Just a few months ago these were $15 grips, the same as any other UM grips. What happens is someone decides to list a set for $50+ and, miraculously, someone buys them. Another seller sees this and prices his at $50+, too, and, as crazy as it is, manages to sell a few. Next thing you know everyone's selling them at $50+ and people begin buying them thinking they're suddenly scarce and valuable and it spirals from there. Don't be surprised to see a set of Uncle Mike's rubber grips hitting $100+ on the auction sites before the madness subsides.
Some folks will remember the same thing happened a few years ago with Tyler T-Grips, some of which sold for $200+! Of course the market eventually corrects and they're back to normal pricing today.