$100?! WTF. Gamestop 3 miles away from me has it for $14.99
Sometimes rare games reach ridiculous price points on eBay. It's not entirely unreasonable, either. Just because your
local Gamestop has it doesn't mean that's true for the people bidding. Are they supposed to travel around the country checking every single Gamestop? It's more likely that your local Gamestop doesn't really understand the value of the game. The number of copies in circulation is small but the audience that cares about it is also small. You're not going to get a good sense of its value by only selling it locally...
That's why you should buy that copy and sell it on eBay. Seriously. It helps balance out prices for everyone, and you can make a nice profit while you're at it.
Oh yeah, the game. I didn't really like Crimson Gem Saga, to be honest. It was functional, but also felt really generic and dull. I never finished it.