Old Rangers are pretty well made in general, but the 3rd generation ('98-2011) were the best. They had two previous generations, and they all are built on the same platform. They started making them in 1983 or so, and updated the original hydraulically controlled transmission with electronic controls through the mid 90s. The 3.0s are generally more bulletproof engines, but they stopped making them in 2007 or 2008 I believe. My '99 3.0 has 285k on it and I drive it between 50 and 100 miles a day. A Ranger with a standard will last longer than an automatic. 

Check underneath for rust. Even if the panels are good, the rear half of their frames is made of considerably poorer quality steel, and they tend to rust out. My truck has spotless body panels, it was a Kentucky and Tennesee truck, so I thought it was clear for rust. I discovered the frame had started to rust through along a hairline crack. A friend welded new plate over it. And it's been fine since. I keep an eye on it.