I did a trackday at Goodwood with my £400.00 Toyota Celica back in September. Same set up as Cadwell by the sound of it, but cost £260.00!!
Worth every penny though. I did feel a bit out of place when the Ferrari's and Porsche's started to turn up, but I did manage to keep up with a peugeot 205 GTi which I was pleased with.
I wanted to take some in car footage, but the track official said that the camera needed to be in a proper cradle, and not held by a passenger. Might be worth checking this out Gaz?
And yes, the insurance for any damage to the track should be included in the price, that's why I bought a cheap car so I did'nt damage the Golf (which probably wouldn'nt have been so much fun as the Celica anyway)