I bought an 850 for a good price last January. Since then I've assembled a long list of things that need attention....maybe not such a great deal after all.
Maybe this list will help you as you evaluate the one you're looking at.
1. Steering very loose. Seems to be play everywhere: at the sectors and at the spindles.
2. Lift needs addjusting and probably some parts. When I put the lever all the way down, the lift arms don't go as low as they should. If I switch it to draft control, the lift arms will drop another 8". Put it back in position control and they come back up.
3. Brakes are not great. My other 850 has great brakes. You're probably not used to having good brakes with an 8N, so you may not even notice.
4. Transmission won't stay in 1st gear unless I hold the lever in place. Since I do most baling in 1st gear, this is a pain.
5. Temp gauge never moves. Either the gauge is bad or the t-stat has been removed. I've worked it pretty hard and I'm thinking the gauge is bad.
On the bright side, the engine fires right up and runs smooth. And the sheetmetal looks really good!