Volvos are not as reliable or as inexpensive to maintain as Hondas or Toyotas. Having said that, when we bought a minivan and had to get ride of a car,I chose to keep our 94 855 and sold our 95 Toyota Avalon even though the Avalon's mileage was much lower at the time, because I preferred to drive the Volvo. Handling seemed much better to me.
If you use the dealership for repairs, you may find that parts and labor are expensive. On the other hand, used cars are very affordable right now because of the economy, and if the price is right and the car is checked out by an independent mechanic, it may still be a good choice for you. Having a complete set of repair records on the car would be helpful. I would be hesitant to buy this car from a car dealer without some kind of warranty or without records, you don't want someone else's headache. If the car has been neglected or abused it would not have much value left in it.
In spite of some of what you might read here on this board, generally the 850 has a good engine and transmission, and if cared for properly should last a long time.