At an Aug. 22 farm auction in Montevideo, Minn., a 1997 John Deere 8300 tractor with 868 hours sold for $95,000, making it the highest auction sale price on a John Deere 8300 in five years.

To illustrate this, let’s examine a common used tractor with slightly more than 200 hp and now 15 to 20 years old—the John Deere model 8300, made from 1995 to 1999. In 2004, the average ...