some friends of the wife have a mk4 Golf TDI (X-reg) with a knackered (automatic) gearbox.

How many variations of the auto gearbox were used with this Golf platform - and how much does a decent box cost?

(excluding labour)

Theyve been quoted £2k inc labour so far!

Bloody heck. I'm sure Newbury Transmissions would quote you a helluva lot less. Auto boxes are pretty easy to rebuild anyway, as long as the torque converter is still in good shape.