I have a Ford 6.0. While that model has certainly given its owners more than their fair share of problems, there is a bright side. These are very popular trucks and many smart, motivated owners and mechanics have spent their time examining them and figuring out the set of problems afflicting the engines. Once these are taken care of (and yes, it is a long list: head bolts, egr cooler, oil cooler, coolant filtration system, oil filtration system, replacement of high pressure oil pump system parts, coolant reservoir cap, etc.) a lot of the owners on the various Ford diesel forums seem satisfied with their trucks. I can't speak to the price of the truck, but clearly how much, if any, of the above bullet-proofing was done is important.
Here are some links to general information about the engine:
http://www.badgertrek.com/sportsmobile/Bulletproofing.shtml - owners of a 6.0 Sportsmobile van listing the repairs and upgrades they made
http://www.utahbiodieselsupply.com/...liter-diesel-biodiesel-mechanics-perspective/ - part 1
http://www.utahbiodieselsupply.com/blog/ford-6-0-liter-high-pressure-oil-pump/ - part 2 of a diesel mechanic discussing the 6.0, more than just biodiesel covered in these two posts
http://www.bulletproofdiesel.com/ - manufacturers of a widely used replacement egr cooler, lots of good information on their website, particularly the 'Information Center' section