https://science.house.gov/sites/republicans.science.house.gov/files/documents/hearings/102611_Musk.pdf

As a result, SpaceX developed the Falcon 9 rocket for a fraction of the cost NASA
would have paid under a traditional acquisition model.

NASA’s internal studies using the NASA-Air Force Cost Model (NAFCOM) concluded that
it would have cost NASA $1.7B to $4B to develop the Falcon 9 rocket.

By contrast, in partnership with NASA’s COTS program,
SpaceX developed the Falcon 9 for approximately $300M.

It bears noting that the Falcon 9’s development included designing,
building and testing SpaceX’s Merlin engine,
the first new allAmerican hydrocarbon engine for an orbital booster in forty years.

要するに：　
NASA が開発したら $1.7B - $4.0B かかるとモデルに基づいて研究されていた。
COTS プログラムのもとでの falcon 9 の開発費は $300M だった。