The Pentagon might be optimistic about getting F-35 costs down is that projected foreign sales of the stealth fighter are likely to be substantially larger than the Defense Department now lets on, meaning that a volume discount is likely to apply in the long term.
Eight F-35 partner nations (Australia, Britain, Canada, Denmark, Italy, the Netherlands, Norway, and Turkey). Those partners have a combined requirement for 700 F-35s; meanwhile, the already-identified interest among those five additional countries totals more than 700.
There are about 4,500 F-16s out there that will need replacement in the next 30 years, on top of Harriers, Tornados, F-18s, and AMXs. A potential world market nearly double the planned US production of some 2,400 F-35s.