I bought a 2000 ZR2 S10 back in 2007 with right at 120K on the odo. I now have over 250K on it and have replaced the fuel pump 3 times, radiator, ignition coil, plugs, wires, ignition module, clutch fan, upper radiator hose, heater core, blower motor, idler arm, high pressure switch on the compressor and 2.5 sets of tires. They are great trucks. Mine leaks more oil than it uses but it does not smoke a bit (about a quart every oil change roughly 4-5K between changes). Oil pressure is rock solid at 35-40psi at idle in drive with 20w-50 oil with Lucas oil additive. Granted most of my miles are interstate @ 75-80mph as it is my daily driver. It is going to need a trans rebuild and most likely an engine rebuild at some point but I am driving it till the wheels fall off.
As far as the body it has rust in the pass lower cab corner and the drivers rocker. Underside stays pretty lubed from the leaks.
I would not hesitate on buying that truck even if it had a little rust as long as the mechanical checks out. Biggest thing you will most likely have to replace are the front suspension parts as the 4wd puts a hurting on the steering components. Mine was rebuilt before I bought it.
Good luck
PM me if you have any other questions on these trucks and Ill try to help.