Sorry to hear about your 850. You are right that finding a 90's model Volvo with a 5-speed is difficult.

Personally, I have yet to see any 5-speed transmissions (M46 or M47) with more than 200,000 miles that work particularly well. Either a synchronizer is shot, it doesn't want to shift into a certain gear very well (internal trans problem, not a linkage problem), the bearings are shot, or something else is wrong with it. Usually it's a real expensive problem to get fixed, and for the same reason it's difficult to find a 5-speed in a car, it can also be hard to find a good replacement in a salvage yard.

But don't let that scare you, just be informed. There's a link in the 700/900 FAQ about test driving a manual transmission and what to look for.

http://www.brickboard.com/FAQ/700-900/Transmission-Manual1.shtml#Test%20Driving%20a%20Manual%20Transmission

Or, if my link doesn't work, choose the option "Transmission: Manual and Clutch" from the table of contents on the main FAQ page. The manual transmission in the 1991 240 is the M47, and is the same as what would be in a 700 or 900.

Good luck!