Subaru quoted me over $400 (+gst) for a new one, and aside from the price I'm reluctant because I can see them going the same way as the originals in a few years.

Just phoned the seatbelt repair guys which sounds like a much cheaper option, although they have to re-web and re-tension the originals rather than supply complete units.

Now have a call into a couple of parts places to see whether there's a suitable after-market replacement from Klippan. Can't find any reference online but will let you know how it goes.