I'm afraid I cannot comment as these type of warrenty packages do not cover a car with mileage above 100,000!
However, the price does seem to be standard across dealerships/car showrooms.
I would say that you should read the fine print and see what it excludes.
Perhaps have a look at other schemes like AA or even Tesco.
I know it's not much help but you might get a better deal looking elsewhere and again read the T&C's.
Let us know how you get on and I'll also move the post to the right area as well.