Without photos and only a description that sounds like a middle of the road truck, I don't see more than $1500. It would help if you could verify the miles and had pictures, but then again, old is old. Age sometimes is harder on something that just sits than something that is actually used.
There are dozens of 3/4 trucks in this area that sound just like you described. What they leave out is that it spent its life spreading feed and hay and living in a barn with the cats and mice. The undercarriage is spotless, because.... well go look at some old farm trucks and tractors that spend a lot of time driving through the pasture, you'll see. Driving around in that tall grass and weeds, especially on a damp morning, does wonders for cleaning up underneath.
