From 2009 – 2010, the US Veterans Administration built a system called the Veterans Benefits Management System (VBMS). It reportedly used agile methods including Scrum and appears to have been a success. Here are some links for further information.
Early report mentions agile. Budget is in the ballpark of $100 Million.
A VA press release from January 31, 2011 indicates the system was launched successfully thanks to agile methods
The Linked-In profile of a person working on the project indicates that there were 12 Scrum teams involved. I am not citing that out of respect for his privacy as I do not know him. Though you should be able to find it by searching linked in for terms ‘VBMS’ ‘agile’