Been to Morrisons at Festival Park, Stoke earlier and they had a Boy and his blob for Wii for £6.99.
Next best I can find is about a tenner.
It was located in the bargin bin at the end of the entertainment section. They had Boom Blox Blast Party for the same price. There was at least one copy of Boy and Blob and two copies of Boom Blox left at about 1pm