I was in sainsburys early evening yesterday and thought i would have a nose at the games.
Much to my surprise i found Lips: Number One Hits Microphone Bundle, which is the 2 Mics + Game bundle for Xbox 360 for £14.99
It is definitely the cheapest around at the moment that i can see, the game was amidst the sale section and there was alot of games in it!!
I couldn't see many bundles out on the shelf but worth a punt at your local store as it might be nationwide ;)
An awesome deal for the microphones alone, seeing as they are £10 for one atm ;)
*INSTORE ONLY THAT I CAN SEE*