quiet a common problem this, i had the same problem with my escort td. i managed to flush mine with the house pipe and a air line, fill it with water and then force the water out with compressed air, ideally in its backwards flow dirrection. mind you, ts still not 100% but good enouph now.
and as to labour, your garrage is about right with the quote as the dash has to come appart and possibly out. a nasty job to do really.