There is a forum search box to the left, and if you search for GNG you will find posts from the past few weeks about them. This will give you some idea of prices. But every transaction is different; I bought mine for far less than recent figures would suggest, yet another player might be willing to pay far more.
the markets kinda died really since the events recently passed. They've lost their twinkle for me now because of it but I'd recommend keeping it for sure LOL as you have an original granted first generation GNG lol : ) It's special and should make you smile each time you play it : )