Definitely not at Gamestop. I checked months and months ago and the guy told me $40. And just as recently as last week, my local GS was still selling scratched-to-hell used DS fat systems for 100 bucks.
It seems original DS systems in good condition seem to be selling for about 80 or so dollars +shipping at eBay. However, if your's isn't working properly, this may not be an option.