Plenty of decent looking mk3 axles on fleabay at around the £100 mark. I would think the problem will be finding something in reasonably good condition at that age (2004). There must be dozens of breakers with them, good hunting.
The labour costs will depend a bit on how easily it goes, working on old cars with rusty undersides can be a lottery, a couple of seized fasteners will slow things, not just having to cut old stuff off but then getting appropriate replacement fasteners etc.
I'm guessing but with all the facilities, lifts, stands etc, and a couple of workers where required for handling, maybe single figure hours?? Five/six maybe? It ought not be too complex, rear beam axles usually drop straight out without having to take other stuff off (exhausts etc) but you never know until you do it. If it came in at £500 it would probably be in the right sort of ballpark I'd guess, depends a bit where you are in the country (rates).
