We had a 1992 7.3...The motor leaked but ran perfect...it was all the other little things that started making it more hassle than it's worth. Little wiring issues, rust, seats getting worn, etc...
I don't know the Idaho prices but you should be able get a reliable truck for well under $30k. Based on local midwest pricing, $15-20k would get us something in the 8-12yr old range that should be reliable. We picked up a pristine 2008 3yrs ago for $10k. It was a V10 and I assume in the mountains you want the turbo that comes with the diesel.
Unless the truck is pristine other than the items listed, you are reaching the point where you can expect new items to wear out regularly.