 The bulk of costs for historical nuclear defense programs have been for delivery and support systems, rather than for production cost of the bombs directly (with warheads being 7% of the U.S. 1946–1996 expense total according to one study).After initial infrastructure development and investment, the marginal cost of additional nuclear bombs in mass production can be relatively low.In the 1980s, some U.S. thermonuclear warheads had $1.1 million estimated cost each ($630 million for 560).