Jim,
They might be £50 for your shopping trolley, but they aint £50 for my car..... and neither are they for most people that run wheels that are actually wide enough to ensure the car can pull the skin off a rice pudding with traction.

Jtechsaff,
I would not use any normal road tyre for a full on track day and expect them to last.... that is what the likes of 888's and Dunlop 01's and 02's are for.