Welcome to the world of expensive belt changes, ive got a Golf TDi 150 and that cost me nearly 700 quid as i wanted the brake fluid and a couple of other jobs doing too
Belt is something like 3 hours or so at £88 per hour plus £70 for the bits thats £335 ish, then the normal service is like £220, so thats £555. Sounds about right to me.
