Either sell it to one of your mates or sell it to ebay. Do NOT, I reapeat! Do NOT sell your DS to EB games or any other video games retailer as you will be ripped off your money so they can make a profit. Unless of course, NZ shops are just unfair. I am not quite sure as I don't use the american currency. How ever sell it lower than the RRP or else your seller will buy a new one at the shop instead. Unless, of corse, your good at persuading or your seller dosen't know of the DS price. And remember, its okay to streach the truth.
Good Luck