It's safe to assume these kinds of estimates are "order of magnitude" estimates, meaning they could be off by a factor of 2 or more. The goal isn't to build you

It's safe to assume these kinds of estimates are "order of magnitude" estimates, meaning they could be off by a factor of 2 or more. The goal isn't to build your own system or to bill the government, it's to put the numbers in perspective. Case in point: if you had asked me if phone recording cost closer to 10 billion dollars or 100 million dollars I would have guessed 10 billion; now I know better. Being able to quickly do order of magnitude estimates (especially in your head) is a very important skill IMO. I've heard McKinsey makes it part of their interview process.