What are the two most cheapest ds lite games?

My friend gave me his 2 year old ds lite when he got a psp, and its got alot of scratches, i bought pokemon pearl and super mario 64 a case and and charger for $130, I realised at ebgames u can trade in a ds lite and 2 games for a new cobalt ds lite which i wana do, But i wana trade in wif cheap crappy games, what ones should i buy