I picked up a 2010 E350 6.0 SDEB with 134k for a bit over $14k about 3 months back. That was about 10k miles ago after driving it home from the NE and a major trip out for the Baja 1k. It has been flawless. I love the van and am planning on getting the pop top from SMB and building it out the rest of the way myself.
During my search the advice given to me by a friend who owns a Ford dealership here in Chattanooga was to look at Ford's service history data for the particular vehicle. You may want to have a Ford dealer search this for you as it is more than your average CarFax. If you find there have been issues in the past, then you should avoid it. If it has no issues then it shouldn't give you any if properly maintained and not abused.
From my research, the 06-07 vehicles are a sweet spot as they were before the EPA clamped down on diesel emissions but after the classic issues with the 6.0 Powerstroke motor were resolved. Anything 06+ is what my target was. I just happened to find a rare 2010.