If i trade in your psp 2000 to gamestop and use it towards a psp 3000 how much extra $ will i have to pay?

my psp 2000 is about 1 and a half years old and has one minor scratch on its screen otherwise its in good condition. i also have 2 movies i am willing to give. also i do not wish to buy the entire psp 3000 bundle with ratchet and clank just the system. plz give good answers!!!!!!!!