Northrop Grumman B-2 Spirit

Also known as the "Stealth Bomber," the B-2 was originally designed for use during the Cold War, and is capable of carrying nuclear weapons. While it was first used in combat in 1999 during the Kosovo War, the B-2 program started in 1979 by President Reagan. The project was extremely expensive. By 1989, an estimated $23 billion was secretly spent. At the peak of its manufacturing, 13,000 people were employed at its dedicated factory in California.

Each plane averaged $737 million (slightly over a billion in today's dollars). The costs of the entire program, including spare parts and research and development, worked out to $2.1 billion per aircraft ($2.87 billion in today's dollars). Of course, that's just the program to build it, not to maintain and fly the aircraft.