I'm not surprised as they were the cheapest in Europe for a long time. They aren't anymore btw. Another Uk site is (creditcard required).
You can view it on this price-comparing website: http://www.budgetgaming.nl/game-profile/ps3+-+gran+turismo+5:+prologue_preorder.html
It will be out, March 28, as well as many other nice games, like God of War.
The Patapon forumtopic: http://www.vgchartz.com/forum/thread.php?id=14103