Being that I am a used game collector, this is something I do not see very often with newer games. Older games, mostly the popular ones from the NES, SNES and N64 era go between $40 - $100 dollars since they are a) obviously no longer being sold and/or b) a cult hit by was discontiuned shortly after release.
This is very strange for Zack & Wiki. I think I saw it at my local EB Games, being sold used. Can't remember the price, but I'll check to see what it was being sold at next time I'm over there.