Just got a retro fit quote from my stealer for £165 all in for each side in the rear seats.
They said you cannot do the front unless you have an airbag isolator switch?
ISOFIX was never standard on a B6. It was still an option when we bought ours in 2004.
IIRC, it was about £80 for them which includes fixings on outer rear seats, front passenger seat and a switch to turn off the passenger airbag.