OK as a mechanic at a Toyota dealer here are some recomendations . 22R tough little motor as long as you do your oil changes . If the oil changes aren't done reasonably regular the timing chain goes and eventually wears through the front cover into a water passage . coolant in oil means a toasted motor. to check for this start the motor from dead cold if it rattles then shuts up the chian is on it's way out pass on that one, or make sure the price drops about a $1000 because that is what it is gonna cost at a shop to fix depending on what the shop you use charges.
If you are looking at a pre 95 the other motor is the 3L V6 , check the water pump they have a tendency to leak and it is driven by the timing belt so it is a bit of a job to do. follow the lower rad hose to the block . If it has Toyota antifreeze in the rad ( it is red ) look for pinkish or red streaks or if really bad something that looks like a corral growth, if green antifreeze it will ust be wet. also the timing belt is done every 96,000 km's so check the front cover for a sticker to tell when it was done last.
the other thing that goes on the 95 and olders are the fuel and brake lines have a tendancy to rust out above the gas tank . kinda hard to really check but at least look to see if they are leaking already.
If you do buy a truck or 4 runner 89-95 stop by the local dealership and check if the center link campaign has been done . I can't remember the exact campaign # but I think It 507 or 508 , it is 5 0 something anyway. also don't dismiss the T100 , if you can find one. They are one tough truck .
and if you find a Toyota newer than 1995 in good shape for under $10,000 tell me where you live because I am coming to your town truck shopping. Toyota's are pretty damn good trucks but they demand a nose bleed premium around here.
Happy shopping
PS as for mileage we had one customer who had a 1990 Toyota 2wd last time I seen it it had almost 800,000 on it the 22r had not been apart for anything bigger than a water pump . but he also did oil changes every 3000 km and always did the maintenance as per the owners manual. I think it rusted out on him .