http://www.spaceflightnow.com/news/n0603/03dawn/

The principal investigator's spin (understandably defensive) is that Dawn was in no worse shape than comparable deep space missions. Also, the 40M over budget was actually a very worst case scenario, and they had quoted 17M as an initial estimate. I hope there was very good reason to cancel this mission so close to launch as it (potentially) would've returned major science (unlike another shuttle flight). Obviously, unless one is directly involved there is no way of determining whether the craft was cancelled due to some level of incompetence (overruns, design flaws, testing weaknesses, etc) or whether it was more politically motivated.