Normally I wouldn't advise resurfacing (or "cutting" or "grinding") rotors, especially Volvo's, because they're typically thin. There is also a legal issue of a minimum thickness, below which you're not allowed to let the resurfacing fall.
Essentially, by removing metal, you reduce it's mass and, as a result, for any given amount of heat energy that the brakes much absorb in stopping your car, your rotors will rise that much more in temperature -- so obviously, this will make your brakes run hotter, something you really want to avoid.
Remember that resurfacing is 9 out of 10 times just a scam to generate more income for a shop. Only rarely do rotors genuinely warp or develop rust spots that need to (or can only be corrected by) a resurfacing.

And if you've decided to do it, why do you think you need it? If it's because of circumferential grooves (i.e., circles) that you see in the surface, forget it -- it's not needed. Volvo, in their "green books", explicitly states that circumferential grooves can be left alone because they do not impair brake performance. You should only consider resurfacing because of unevenness or runout, particulary if it's felt in the brake pedal.

This said, I know that money can be tight (are you a student, perhaps?) and this might be tempting. Then I'd suggest trying to find an inexpensive vendor to get the rear rotors -- they can't be much more than what you'll pay for the resurfacing.

Good luck.