How much?
That seems absolutely insane to me...
My belt is due, I personally buy the kit myself as I have a friend who works in a motor factors therefore I get them cheap but none the less I recall only paying in excess of 200 for labour and that included the supply and fitment of a intercooler pipe, my local garage is cheap... but not 400 pound cheap lol!
I would suggest getting another quote mate, would also be good to find out how long the book time for a belt change is as it will give you an idea of what labour time you should be paying....