I need help buying a Cummins.

250K isn't a whole lot, from my experience the biggest problem these old trucks have are with anything not involving the drivetrain (aka the rest of the truck) My uncle recently sold his 1996 12V dually that had 380K on the clock and ran like a top for $6,000. He was a diesel mechanic and was the only owner so he knew how to maintain it, but he always said the most maintenance that he did on that truck was replacing burnt light bulbs or broken plastic interior pieces. My father owns a 1998.5 24V and the most maintenance that has been done has been replacing electrical sensors. Point is, don't discount the older trucks just because they are "old", look up videos online on how to buy one of these and determine improper maintenance (checking blowby is an easy one), and good luck! I guarantee you'll find a truck you'll love with a little patience