As everyone says - First deal so go easy on me! ;)
Was in Sainsburys in cannock today when I noticed WOTLK for £15, Took it to the till and it came up as £6 - not sure if its nationwide or not but worth a shot for you nerds out there! :D
Edit - Its around £25 off the World of Warcraft Website and still around £23 in game last time i checked.