B-2 Spirit: $2.4 billion

The B-2 bomber was so costly that Congress cut its initial 1987 purchase order from 132 to 21. (A 2008 crash leaves the current number at 20.) The B-2 is hard to detect via infrared, acoustic, electromagnetic, visual or radar signals. This stealth capability makes it able to attack enemy targets with less fear of retaliation. In use since 1993, the B-2 has been deployed to both Iraq and Afghanistan.