Just found this one:
http://www.evalbum.com/2898
To my knowlege, this is the worlds first conversion of an F250 (4x4 no less!!!). Just don't look at his build cost....
1978 with C6 and 7.5L V8.....gotta love that era. Smallest/lightest truck you could get in the F series and yet available with the biggest engine and toughest tranny. You could even buy crazy highway gears like 2:1 or lower than 4.10 if you wanted. These days, you buy what they sell you.
That truck might not be too bad to convert if you are comparing against a new ranger. 1970s F150s are fairly light. Not as light as 1980-1983 with the swiss cheese frames, but still pretty good. Frames are also strong enough to take the load.
Getting something that can do 70 MPH on $5000 might be a challenge though. The 1970s fords look great IMO, but they don't have much going for them at higher speed. Did Randy get back to you yet? I suspect motor and controller will already use up nearly all of your budget.