If you're buying or trading for cart only, make absolutely sure it's not a bootleg! That's one game where you definitely don't want the bootleg battery dying on you! There was a thread somewhere on the boards about how to identify a bootleg.
I see "Golden Sun: The Lost Age" new at every Toys'R'Us for $19.99, although maybe there are not that many in South Dakota???
BTW, cool avatar! Gunstar Heroes is my all-time favorite game! So much I named myself after it!