When I bought mine it was around 25 dollars, with shipping it totaled around 30. It's a nice investment, a great game to add to your pokemon collection.
I got mines off ebay, but you really have to screen it well to make sure you're getting a legit copy (and make sure they allow returns), but yea that's about the price.
I think the key to knowing if they're legit is if you can pal park with it, and the DS game recognizes it (so you have to have a DS or DS Lite to do this check).
Im sorry, but I find this funny. If you were to come to my town, game stop has new and old copies for around 5-10 bucks
