According to wikipedia: Avionic came from the F-16, F-15 and F/A-18 programs (unsourced claim, but very likely, those parts were purchased as spares for those

According to wikipedia: Avionic came from the F-16, F-15 and F/A-18 programs (unsourced claim, but very likely, those parts were purchased as spares for those aircraft). Engines are modified are modified F404s drom GE. That leaves the airframe, landing gear and some other bits and pieces like evironmental controls, but the avionics and engines account for the vast majority of aircraft costs.