5.9 Cummins trucks in the 04-06 years are gold money wise and honestly...the automatics suck so unless rebuilt, plan on a built trans with the mileage you will find.
Early 6.7's cost less due to emissions issues BUT, make more power, have a better transmission and can be deleted to run like a 5.9! You can be into a great sub 100k 6.7 for your price range that is ready to rock. I'd be willling to part with mine...deleted, tuned, ready to haul...
7.3's are good but slow and hard to find one with less than 150k for a decent price. Owned one...they are slow but reliable.
Cummins all the way!