Don't think this will rise much in temperature if at all but I've been waiting for this to drop below the £10 barrier so have just ordered through Quidco with a Walkers code so probably looking at just over £8. Quick scout & its very expensive elsewhere.
Appears to be the 1-disc directors cut from the cover which is seemingly less available than the 2-disc version (personally disc 2 very rarely gets a spin in my experience anyway)
edit. Blockbuster appear to have the UK Exclusive 2-disc + digital copy version for £10 as an alt for the more hardcore: http://www.blockbuster.co.uk/product/blu_ray/watchmen/223893.htm