The development costs for Falcon 9 v1.0 were approximately US$300 million, and NASA verified those costs. If some of the Falcon 1 development costs were included, since F1 development did contribute to Falcon 9 to some extent, then the total might be considered as high as US$390 million.[14][2]
NASA also evaluated Falcon 9 development costs using the NASA‐Air Force Cost Model (NAFCOM)—a traditional cost-plus contract approach for US civilian and military space procurement—at US$$3.6 billion based on a NASA environment/culture, or US$$1.6 billion using a more commercial approach.[15][14]
https://en.wikipedia.org/wiki/Falcon_9_v1.0
Cited from https://www.nasa.gov/sites/default/files/files/Section403(b)...