One new rotor costs $60.50 at www.volvoparts.com. I think
you are better off to buy 2 new ones. As a general rule,
Volvo rotors should not be turned, de-glazed, or machined.
Still, don't know if that would fix the sqeeling problem or not.

Also, I assume these are not the original rotors since front
rotors need replacing around 60K-70K miles. If they are original,
then I would not even consider anything but replacement. If
they are not original, then I assume they are about half way through
their life and will need replacement in 30K miles (next set
of front brake pads). (They should be measured to determine how
much life is left on them -- minimum size is stamped on the edge
of the rotor.) In the second case, I still think it is
cheaper to replace now ($121) since you will be buying new
ones in a couple years anyway ($75 now and $120 in two years).