Can't comment on the price, as it really varies on where you live.
Only real big problem with the Nissan Hardbody's, aka "Nissan Pickup" (and the Pathfinders) is frame rust if it was driven in an area where they use salt on the roads. Go under the truck with a screw driver and poke the frame to make sure it is solid.
Other than that it is just regular stuff to look at for any vehicle. If your friend is really unsure about the mechanical shape of the truck, spend the $40-50 to bring it to another mechanic to look it over first. Might have to drive it over, or bring a mechanic friend to look at it.
Parts for the truck are VERY easy to obtain and pretty cheap in most cases. A great aspect is that many parts from a pathfinder of the same age range will transfer over no problem. Engines/transmissions are the same used in the pathfinders, as are the interiors and some of the front body panels.
Engines of that age are pretty bullet proof and will generally last longer than the rest of the truck. And like I said above, if you have a problem with the engine/transmission, you can pull one from a pathfinder (if you can't find a hardbody) and just drop it in. At 70K miles, that engine is only just broken in. You will easily get well over 300k miles on it no problem as long as it is properly maintained.
Auto hubs are nothing but problems, but that is easily fixed with a set of manual locking hubs. You can pick up a used set of OEM manual hubs for them pretty cheaply, or just buy new ones from Warn or MileMarker for $80-$120. Takes 15mins to change them over.
If possible get some pictures to post them up and I could give you a better impression of the truck.