Not very good prices are they,i got £100 for my Xbox 360 from Blockbusters the other month when i decided after the Microsoft Xbox One reveal i no longer wanted anything to do with them as a consumer.
Best deal i ever had regarding trading a Playstation 3 in was when they first introduced the slim edition,took it to Gamestation who apparently had to match CEX price and i got £220 for it against a new Slim Playstation 3 which i think i ended up paying £30 for it.
I think even those prices you quote will tumble even further when we get closer to the street release date and the fact i see Game inundated with Playstation 3 and Xbox 360s .