We own 2 older 700s too and they're great but I now repair mostly FWD 850s, X70s daily so I have alot of experience with them too. I'd say that an early 850 in good condition is still a very good car and I believe that you can find them for less than 10K if you're patient. If and when the occasion arises, I'll buy one myself. Now, if you read many of the threads here you'll notice the AC evaporator threads and sure, it's been a problem BUT I wouldn't let that in itself be a decisive factor. If funtional AC is critcal to you, then do check its operation and see if it's still got its original evap which is obvious by looking for 2 white plastic rings where the pipes go through the firewall. Only factory evaps have those so if you see them, the car still has its original evap.
Now, manual trans 850s and X70s are NOT common in 850s but they're out there so if that's important, your search will take longer and you might even want to consider E-bay and travelling to look at it, not an all bad thing as some might think as I've done it and would do it again if I want another unusual car.