No-one will ever accuse me of being a gifted mathematician, but surely so much money - and R & D effort - has gone into the F-35,( alright the 'B' may have a slight question mark, personally I think will prove very us......to turn down at this stage ?
McDonnell Douglas A-12 Avenger II 
.......The aircraft suffered numerous problems throughout its development, especially with the materials, and when the projected cost of each aircraft ballooned to an estimated US$165 million, the project was canceled by then-Secretary of Defense, Dick Cheney, in January 1991......
After the cancellation of the A-12, the Navy elected to buy the F/A-18E/F Super Hornet, which replaced the A-7, the A-6, and the F-14.....