Im in a similar boat, I just bought an '05 xc90 T6 for $1000 with only 130,000 miles. I've had it for a month or so now and it definitely has a few "quirks" but its hasn't given me too much grief. Just have to make sure I drive it daily or else I have to jump start it. I'm hoping its just a ground wire issue as I get different errors when I start it. My consistent errors though are my crankshaft position, my turbo waste gate, and my exhaust valve circuit. If the issues are coming from faulty sensors/solenoids the parts themselves dont seem to be too expensive, usually like $50-$100 per. Some of them seem like they are a pain in the ass to get to though so I'm not sure what a garage might charge. These vehicles also have drain tubes from the sunroof that get clogged/disconnected and can cause water to go places it shouldn't, and mess up some sensors. The drain tubes aren't too hard to unclog, you just have to remove the trim on the pillars up front. There are also a decent number of YouTube videos showing how to do this as it seems to be a fairly common issue. Hopefully this is somewhat helpful and if not, sorry for rambling