seems like way too much for me. I just had about 1600 bucks worth of work done to my 850 and cleaning the PCV system was about 150 bucks of it mostly in labor.

mark
96 850T

If the PCV breather box under the intake manifold is plugged, the intake manifold must be removed to replace it, it can't be unplugged as it's got chambers that aren't easily brushed out with solvent. Gunk can collect inside those and solvent won't unclog it. That's then a bit time consuming. The only time those ever plug is if the owner fails to change oil often enough because otherwise it simply doesn't happen. They're not talking about the flame trap as that's a common maintenance item that should be checked, replaced every 30K miles.
$600 seems a bit steep for that in itself so I'd also assume that they're doing more than just the PCV breather box and flame trap related hoses.

lack of oil cahanges usually plugs pcv systems, on your car u have to remove the intake manfold to replace the breather box and all the hoses, it is major surgury as i have done it many times and 600 sounds about right. if u dont do it u can blow oil seals and that gets very expensive

This page tells you how to replace the flame trap:

http://volvospeed.com/Repair/ftrap.htm

Well there is no PCV valve, just a flame trap. To replace the hoses and flame trap should add up to $30 if you are using volvo oem parts. Really there isn't much to it, a vent out of the valve cover that goes to the flame trap ($1 item and can be cleaned with carb cleaner and is as good as new) and a couple of funky elbowed rubber fittings that lock into the intake throttle body snorkel. I'm assuming they are doing a whole lot more than that.