PS3 how much for trade in?

shiny black 80gb Ps3, not even a year old. Still under guarantee, well looked after. 7 games Fifa 09, Call Of Duty 4,Killzone 2, Resistance 2, Grand Turismo 5 Prologue, Motor Storm and Haze. 1 wireless controller 1 wireless headset. Original box with receipt. All leads included, pick up only. Reason for me selling this, its because i resently sold my Xbox 360 to buy a Ps3 but i prefer Xbox, so now need the money to buy another 360. SO HOW MUCH WOULD I GET IF I TRADE IT INTO BLOCKBUSTER OR GAMESTATION OR SOMETHING ?? Thanks.