Although you'd be wise to swap over the water pump for one with a metal impellar at the same time as changine the cam belt.....water pump can;t be done without changing the cam belt and the water pump is a known weak point of the 1.8T engine.
Cam belt and water pump is about 4.5hrs labour (half day) @ £45/hr 'ish say £200 add £50 in parts ish plus VAT.
Therefore say to your mate you need £300 off the price to cover that
Otherwise not a bad price.