Midas wanted $650 to change all my pads and rotors. I quickly declined and took my car back from them. At that time, I just changed the pads myself and left the rotors on. They had a lip, but were fine otherwise. It really didn't bother it to keep the slightly worn rotors. Now, a year later, I'm getting the reduced stopping power. So I've bought a set of crossdrilled rotors and mintex pads for about $250 total and a set of steel-braided brake hoses for $90. I'll happily do the labor myself and I'm still saving $300 based on that Midas price (not to mention this is now upgraded parts and even the addition of the braided hoses).

With automatic transmissions front pads go about 30K miles.
If you have a manual transmission you could get up to 60K (I almost
did on my 98 S70 with a manual transmission). If you have 60K on
them with an automatic then that could be a record!

Front rotors are good for two pad changes. Rear rotors last a lot longer.

A set of pads is about $45 and rotors about $65 (each) from a
parts discounter like www.volvoparts.com. Labor to replace pads is
under an hour and maybe 1 to 2 for pads and rotors. Can't estimate
price since labor rates vary widely. Brakes are actually pretty
easy to service and a possible do it yourself job if you
are so inclined. http://volvospeed.com/bay13.htm has instructions.