I'm on 150,000 with my 1997 4.6, original engine and so far, no problems and I drive it every day. That said, I have read of many that fail long before this kind of mileage. Firstly, remove the expansion cap, and check the coolant level and colour, leave the cap off and start the car, check all electrics, front windows should be one touch up/down as is the sunroof. Turn on AC, press the AUTO button and then go back to coolant res and make sure there is nothing coming into it, i.e. gasses, the coolant should be still and smooth with no swirling, if all OK, put cap back on and check all doors including tailgate open. Note that the fuel filler cap will not open unless the car is switched off. Now back into drivers seat, is the AC working ok? No book symbol on display? Set temps to LO and make sure cold air is felt, then set temps to HI, again check temp is hot. Now press the manual air flow buttons in turn, both sides of vehicle should have air blowing in the direction you have selected. Now check drivers footwell carpet for dampness or residue, pay attention around transmission tunnel area, wet/damp sticky carpet means "O" rings have failed. If any of the above fail, then it's best to look for another as there are plenty to choose from currently. This is just a small section of some of the things to check. All ride height options should be tested, these will only work with all doors & bonnet closed, from lowest mode "access" to highest "extended" should take no more than a couple of minutes, any longer and either the bags are worn, or more likely the compressor is worn out.
Some of the above jobs are easy repairs and well documented but as has already been mentioned, it is a buyers market, so get the best you can, with as much history as possible.
