Trump rants on Twitter about "$4bn" Air Force One replacement

The consensus seems to be that the total cost of the Air Force One replacement program will approach $4 billion. Here’s Politifact’s breakdown of the project cost: http://www.politifact.com/truth-o-meter/statements/2016/dec/06/donald-trump/fact-checking-donald-trumps-tweet-air-force-one-bo/

Looks like current estimates are for $3.73 billion over 12 years to produce two airplanes, assuming no budget overruns. The hell of it is that technology is evolving so quickly that whatever we budget for in 2016 will be obsolete by the time these two airplanes exist. I can’t imagine how difficult it would be to work on a project like this.