I'll have to second Jeff's suggestion on the f 250 series. I have a 2000 Excursion with the 7.3 L diesel, and it has over 160,000 miles. Lots of pulling power and no problems thus far. Great vehicle for towing--I can lie down in the back and nap while Marie drives, even with lots of gear aboard the truck.
Last year the new Dodge 3500's Dually were about $30,000 for a nicely outfitted truck--haven't looked recently.