You guys are thinking about this all wrong. The original budget may have been $400m, but here's what will actually happen:
1.) Bids will all come in at $200 million
2.) One of those bids will be selected
3.) The costs will explode to $800 million
4.) The powers that be have 0 understanding of the concept of throwing good money after bad, and since there is already $200m in the ground for foundations/steel/whatever, it will be finished with money taken from somewhere else.