I purchased BURN AFTER READING on DVD yesterday from the FOPP store in Cambridge for a mere £4, which I thought was bargainous, considering it is quite a recent release, and in my opinion not a bad film. I am assuming this is nationwide, as it was under their summer offers. There were LOADS on the shelves.
The next cheapest I found was £4.99 on HMV.com (£4.49 with student discount) - which has already been posted.
Hope this helps someone (go easy - it's my first post)