I don't understand getting caught up on the milage game. I've never based a vehicle purchase decision or price point on milage. It's just not a good indicator of wear and tear. High milage often means lots of highway driving, which can put siginicantly less wear on a vehicle than stop and go driving can. IE - Low milage vehicles. Especially with a Diesel.
Anyhow, if the truck is in the as described shape I would jump on it. With all the problems the latest Navistar (international) Diesel engines are having, Im sure that truck would prove itself to be hella reliable even compared to a brand new truck. I couldn't see paying that price for it around here, but then again our trucks don't rust out in a few years...