Unless you need to tow, I would play the law of averages on this one. There are a bazillion 850/V70/S70's on the roads and in the boneyards. The odds of finding one that meets all or most of your requirements is much higher. If you need a few parts here and there, they will be easily obtainable from your local PnP or one of the national wrecking yards.

Please keep in ind that there are known problems with these cars (ABS pump, AC issues, etc) just like with the 2/7/9 series so go well armed with a list of problem areas to pay extra attention to. Also keep in mind that they are interference engines so the first act of maint should be changing the timing belt unless you are willing to bet the cost of an engine replacement on the information the PO gives you regarding the last change.