Just saw on Slickdeals, if you trade in your existing DS system for credit towards a 3DS. An XL will get you 100 bones. Others vary in price starting with 40 bucks for a DS Lite.
http://slickdeals.net/forums/showthread.php?sduid=270734&t=3198258
http://slickdeals.net/forums/showthread.php?sduid=270734&t=3198258