By what factor did SpaceX reduce the cost of developing a rocket comparable to the Falcon 9 compared to NASA's estimate?

Answer

A factor of more than ten

NASA estimated developing a comparable rocket system would cost around $4 billion, whereas SpaceX achieved a comparable capability for an estimated total investment of roughly $390 million across the Falcon 1 and Falcon 9 programs, resulting in a cost differential exceeding a factor of ten.

By what factor did SpaceX reduce the cost of developing a rocket comparable to the Falcon 9 compared to NASA's estimate?
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