Despite only being around for the past 10 years, there have been 3 generations of the Expedition. The first generation was made from 1997 until 2002, the second from 2003 until 2006, and the third starting with the 2007 model year. The first two were based on the U platform, with the third based on the T1 platform.
The engine options on these SUVs has ranged from a V8 to a... well, V8. The latest generation adds some diesel V8 engines, along with a Modular gasoline electric hybrid.
You can find these SUVs on the used car market, although not that many since they are only 10 years old at most. Try checking the listings on eBay. Those tend to seller for less than used cars in the "real world".