I paid 2500 for my truck 2 years ago. About the only good stuff on it was the frame, engine, trans and axles.
If I was you I wouldn't pay all that much for it in that kind of condition. $1500 maybe. Once you get into needing to replace stuff like the cab it turns into a pretty big pain in the butt and will be costly if you don't have the ability to do it yourself. And that's even if you can find a good cab that won't cost too much to get home. There are lots of good cabs out there but they never seem to be within 500 miles.