Government accounting is a notoriously slippery and manipulative process. By switching around just a few numbers it is possible to add or subtract billions of dollars from the books.
Whenever I hear government officials quoting numbers about how much a project will cost or how much money will be saved I always take them with a grain of salt. Frankly, they are politically motivated. If the want it to look cheap they can make it look cheap. If the want it to look expensive they can do the same.
Luckily there are a few good non partisan relatively objective sites out there which can help you get closer to the real numbers. Without responsible citizens like these keeping an eye on the way the feds actually govern there is no telling what they wold be able to get away with.