I have a question about selling DS games?

I have five games for the Nintendo Ds that I'm planning on selling. My Sims, My Sims Agents, Dogz, Drawn to Life the Next Chapter, and Pokemon Ranger. I also might sell Mario vs Donkey Kong: Mini-land Mayhem, if I can find it, so I actually have six. I need to make between $35 and $50 off of these games all together, because I am saving up for a summer project. So, my question is, how can I get a good price for my used games. And I hear that Gamestop only buys games for like $2, is this true??