I think the biggest question in buying a used one with over 100K (or really any used car to speak of) is how it has been maintained. If the owner has records to show oil change intervals and regular mainteance has been performed otherwise then you should probably be relatively safe in purchasing a high milage used one.
My '93 is about to turn 162K miles. It has had the head gasket fix performed by a dealer. The alternator was replaced last year and the only other "pricey" fix was a speed sensor went out causing the anti-lock system to light up. Rust started appearing on the rear wheel wells 2 year ago. Past those issues the truck has been problem free. I had planned to trade it in on my '06 SE, but it was worth more to me than to the dealer so I kept it along side the new one. I just put a new stereo in the '93 with Sirius and iPod adapter so I plan on keeping it for a while more, especially since the Revo's still look like they have 50K of tread left in them.
Good luck in finding your machine.
