£350 for an indie is a fair price, when a mates doing it you have to bear inmind that his only cost is his time.
i used to do belt swaps in my spare time and charge £150 quid on the tdi pd engines:
£50 for the parts (genuine parts bought through work at trade price, back then anyway)
2 hours of my time
The tools i already had
an easy saturday afternoons work for £100 - and try to find a garage that'll do it that cheap (or a decent VAG technician for that matter).