2003 A3 8L 1.9 tdi 130 - belt / service prices

Prices obviously vary across the country, where abouts are you?. I would suggest replacing the water pump as well if it hasn't been done. Only another £35-£40 on top. The cambelt drives the pump. Anything happens to the water pump bearing and the belt is off. Original pumps have plastic impellors which I am not a fan of they have a habit of splittingh .I would ask for a metal one.
Also be a good time to change the coolant out and make sure theres enough G12 in there.

Karl.