DP's are nice but so are the Gassers. The maintenance is easier and you can do almost all if it your self. If you don't need to pull more than 5K then a gasser would fit the build and you can new one with all the bells and whistles of a DP.
If you must have a DP then there are lots available to fit the bill. As far as a DP before 2006 that is because of the DEF in all of the new ones. Don't let that stop you from looking at newer DP's. The DEF is not an issue because you should only have to fill it about every oil change, 10k miles and even if you do there is plenty places, every Big Rig fuel station at the pumps, to do so.
The key is find something you like, test drive it, make the deal and get on the road.