It uses regular gas.  It has an anti-knock sensor so that it is very
tolerant of gas octane.  In any case, if you want to experiment, run a
tank of hi-test and a tank of lo-test on a trip at a constant highway
speed and see if you get better miles/$ with one or the other.  Go with
the most economical.

The routine maintenance schedule and standard pricing is available on
Volvo's website at:

http://new.volvocars.com/ownersdocs/2004/2004_XC70/04xc70_00.htm

http://new.volvocars.com/ownersdocs/2004/2004_maintenance_charts/2004_mai
ntenance.html

http://new.volvocars.com/loyalty_v2/sm_02_t3.asp

My dealer publishes prices for each recommended maintenance.  On my '01
XC70 the interval is 7,500 mi.  The odd intervals are just oil & filter
changes.  Then every 15,000 miles they check everything and replace
whatever is scheduled to be changed like belts or fluids.

No more expensive than most other cars, but there is a lot more to
maintaining a car than oil changes.  The Volvo AWD is pretty trouble
free.  You can save money if you have the tools and equipment by doing
it yourself.  The Turbo takes premium gas, but your owners manual and
the inside of the gas cap cover should also note this.