The water pump is about £40, the rest is labour, which is why it's unfuckingbelievable that they don't just replace it as a matter of course when doing the cambelt. Otherwise you end up having to pay all the labour again just to fit a £40 part (ahh, I think I just answered my own question!)
Don't get it done at Audi, they charge £90+ per hour, find a good specialist and it'll be half the price.