Mega Man is the rarest Game Gear game I know of, and is only worth maybe $40 or $50, and there are a lot of Mega Man collectors out there too. If it sells that low, I'd assume that most hard to find game gear titles are only worth about $15-$20 tops. If you're sure it's hard to find, hold onto it. In a couple years when there's an accurate rarity list, you may really have something there.

-Hitman-