This site is gives a pretty accurate value of games.
Video Game Prices & Values | PriceCharting.com | VGPC
Free Video Game price guide with PSA, BGS & ungraded prices for hundreds of thousands of <no value>s. Search for Video Games, browse by <no value>, value, and popularitywww.pricecharting.com
Didnt know that much about it. Sounds like you got some money on your hands. I would hold on to it myself.