Officially, and conveniently, the price tag has been classified. But even by Washington standards, where “black budgets” are often used as an excuse to avoid revealing the cost of outdated spy satellites and lavish end-of-year parties, the techniques being used to hide the cost of Mr. Trump’s pet project are inventive. Which may explain why no one wants to discuss a mysterious, $934 million transfer of funds from one of the Pentagon’s most over-budget, out-of-control projects — the modernization of America’s aging, ground-based nuclear missiles.