I had the rear one done last year. Parts and labor at the Volvo dealer was around $400. Of course, this included tax, environmental and disposal fees and all the other usual BS charges that are part of going to the dealer.

Check Bay13 instructions for diagnosing and changing it ... Others have reported here that the part can be had for about $175 and the job is not all that difficult.

The only caution I'll give you is that if there is something else besides the actual sensor bad (vacuum line elbows or sensor connectors), it's a lot of ca$h that might not have had to be spent. Eliminate the cheap stuff first.

I also seem to recall someone cleaning theirs with a propane torch and some type of cleaner and restoring some function to the sensor. Might be worth a search to find that posting.

Best of luck!