Spending $US15,000 or even $US17,500 on a collectible Nintendo Entertainment System cartridge, that we can understand. They're covered in gold! But $US20,100? That's simply too much, even factoring in Nintendo Campus Challenge 1991's rarity.
But spend $US20,100 on said ultra-rare NES game someone did, snapping up the "one of a kind" item on eBay. That purchase price may not be as outrageous as you're thinking.
It does have three games on it, Super Mario Bros. 3, Pin-Bot, and Dr. Mario, helping to defray the cost. I'm fairly certain that any copy of Super Mario Bros. 3 costs about ten large anyway, so it's a steal!
The real story is that this really may be the only cartridge of its kind, created for a nationwide college video game tournament from 1991. The Nintendo Campus Challenge 1991 was allegedly supposed to be destroyed at the end of that promotion, but one employee managed to hold on to a copy.
Hit up eBay to marvel at this gorgeous little contraption of chips, PCB and plastic.
Nintendo Campus Challenge 1991 NES World Championships [eBay - thanks, Billy!]