Though i dont own s80, I do own 2003 xc90 t5 and 2007 s40.

I would imagine the maintenance cost around the same. Just dont send service @ FA once the warranty finish. Unless you want kena slaughter.

-My xc90 already 13 years old. mileage around 280,000(ish)KM . Basically engine still the same, turbo still the same (however start to slightly leak already), gbox are also the same, AWD system including the driveshafts still the same

-just recently (within this year) front right abs sensor failed (rm3xx) , engine impulse sensor failed (rm350x2) and crank sensor were replaced even though still working, for the sake of reliability (forget the price) and alternator (rm1600 brand new) . I consider it OK, because all of this part has been functioning since the car left its factory in 2003.   

-around 190,000KM (2012/13) all four shocks leaks    so had to change it all, front (rm8xx per side and mount rm1xx per side) rear (rm1400 per side nivomat type    ) , 1 off the reverse sensor failed (rm2xx)

-did change electric fan, not sure when.

-of course through the years of owning it, I also did other normal wear n tear parts change such as timing belts, eng mount, brakes stuff, arms and bushing n etc

-Overall I'm really satisfied with the xc90, I planned to keep it for another year or two than replaced it with XC90 Thor    (but I admit, sentimentally I feel very hard to let go my old XC90)
-For 2007 s40, its relatively low mileage (currently around 79,xxxKM) Two unexpected parts that I have to change was coolant expansion tank (rm1xx) and it's driveshaft (rm5,xxx both side, brand new, original) I believed there was a design defect with the driveshaft when the car rolled out from the factory, during replacement, my mechanic measure the new original Volvo driveshaft was about 2mm longer than the one factory fitted driveshafts.  To be honest, I could go with 2nd hand driveshaft to keep the cost down, but I planned to keep this car at least for the next 4-5 year.

-compared to my Bmw's, Volvo's are easier to take care, no silly eccentric German engineering crap to deal with. The downside is, unlike german car which got plenty OEM and recondition parts in Malaysia, Volvo are slightly harder to get (that why sometime I prefer to stick with original volvo part).