The game is extremely rare, so rare in fact that in an auction last month on eBay, a sealed NTSC copy of the game still in its original shrink-wrap sold for $42,000 - $41,977 to be precise - thus making it one of the most expensive games ever purchased. Games like Stadium Events are now so rare and highly prized that valuations and assessments are not only common place, but a necessity to prove their authenticity and origin.
According to previous auctions, a standalone cartridge with no packaging or the like for Stadium Events fetches in and around $10,000 whilst ones with the packaging and manual can sell for in and around $20,000. The Video Game Authority, which assesses the quality and value of said games, rated this particular cartridge at 85+, which is pretty much near-mint condition.
According to a report by Kotaku, the game was originally placed on eBay and the winning bid didn't come through - however, the seller was then contacted by a serious collector who forked over the money to secure the game for themselves.
While $42,000 is a lot of money for one single cartridge, it's a long way off the highest price ever paid for a game. In 2008, a collector paid $500,000 for an Atari 2600 game. Why so expensive? There's literally only one copy of it in existence.