Not too sure about the trade in options, however i know Asda are selling it for £ 34.97, Argos are selling it for £ 35.99 and apparently ( i have yet to confirm this myself) Morrisons are selling it for £ 29.99.
The only thing is, most of the supermarkets seem to think it is a Friday release date, and as such wont sell it until tomorrow!
I believe the likes of Game, Gamestation & HMV etc are selling it for £ 39.99.
Hope this helps a bit.
**EDIT - why does the new forums not show spaces between my paragraphs anymore?