Woah, it did shoot up! When I traded my copy more than a year ago, I traded the 4-disc complete copy with the giant box for a mint Kingdom Hearts: CoM + guide. I thought it was great deal at the time, and it was... but it would've been better if I kept it now. Ah well.
I had a compendium of the Greatest RPG Archives that I bought for $10 at Kaybee some years back. That shot up in price, and I sold it for like $60 or so as well, considering I never played it (old school PC RPGs, like Wizardry 1 - Gold; M&M, Stonekeep, etc)