This game was released in 2008 (as you stated), so therefore you aren't going to find it on the store shelves anymore. That doesn't mean that it won't popup from time to time in a store if they happen to have some in stock, but generally the game has just run is course. While I don't know if this game can be considered "rare", people on Ebay, or anywhere really, like to make big money on anything they can get their hands on to sell, or so I've noticed anyway. Don't take that as a solid fact.

Good luck on finding a copy if you haven't already! You just need to keep your eyes peeled and hope that a reasonably priced copy shows up.

On ebay they are also outrageously priced as well. Usually over $40 used! This is a 5 year old game now!
Even Spyro, the oldest in the series, is more common to find.