I've just had the belt changed on mine by a none-main-dealer.
The garage came recommended by a mate; it's a performance VW/Audi garage and I had a walk around before I got a quote etc. What this guy knows about VAG cars is incredible.
Cost? He did timing belt, tensioners and water pump for a fraction over 300 quid which i'm pretty sure is very competative.
It's not a straight forward job; a couple of engine mounts need removing to allow the enging to be moved for access, so I guess my point is just be careful with backstreet garages, for the sake of another £100 you could have a lot more faith in the work.