Zavvi have the Foo Fighters - Live At Wembley Stadium (BLU-RAY) for ONLY £10.
Release Date : 17th Nov 2008
If you search for it on their website, it comes up as £13.95 but click on the link and its £10.00, adds to basket and checks out as £10.
Looks to be the cheapest price for this pre-order.
Good price and not much more than the standard DVD version.