How much is my psp worth?

Ive had it for about 2years but i havet really used it,its grey and im selling it with 3games..Ratchent and Clank:Size matters,Sims2,and harry potter and a movie National Treasure2 my friends is willing to pay 50 for it...is it a good deal (im not going to game stop bc i know they rip ya off)