Another vote for the 3rd gen with 5.9, 2003 to 2007. the 3rd gens power, brakes, and stearing are MUCH better than the 2nd gen and you get a USEABLE back seat. I would only go with the 6.7 if you go with the 4th gen but that is out of your price range. Stay with the 6 speed, I never was a fan of the 4 speed auto. If you do go with the auto plan on rebuilding it right after you buy. If its doesn't need it that is good but it seems like every one I have seen the transmission is on it's last legs when it is sold. A GOOD rebuild can run over $4,000 depending on you needs/wants.
Be aware that the 3rd gens do have injector issues with higher miles. Fuel quality and filtering are very important and have a big impact on injector life. The problem is price, $400-600 EACH for new, and you really are gambling if you buy recon injectors.
If a dually can work for you Gonzo's would be a good one to look at. He has been around a bit and knows about these trucks. I will tell you right now the manual transmission trucks are hard to find and the price reflects that. A friend just sold a 2006 mega Laramie 6 sped with 215,000 mi for $30,000. The guy flew out to Oregon from back east to buy it. It did have a lot of work done to it thought, new injectors, front axle redone, new brakes and a south Bend street dual disk clutch.
Good luck on your search. There is a buyers guide on this site that will help with what to look for on each year truck