You are probably talking 130 for a Cam belt kit (minus a discount ) say £100 + about 2.5-3 hrs Labour which can range between £40-100 an hour. Make sure you use OEM Audi parts and fit a new water pump too (circa £30ish)
All in I reckon you're talking anything between £3-500. Whatever you do do not just replace the Cambelt on it's own IMHO!!!