Warplanes are expensive, not just to build, but also because of the tremendous research and development costs. Some current examples are; B-2 bombers which cost $2.1 billion each, C-17 transports are $329 million, C-130J transports are $117 million, V-22 tilt rotor transports are $110 million, F-35 fighters are $104 million, E-18 jammer aircraft are $96 million, F-18 naval fighters are $95 million, MH-60R special operations helicopters are $44 million, while the MH-60S model is $29 million each.
It notes that the per unit excluding R&D cost of the B-2 bomber was $400 million, and once you have sunk costs, there is good reason to look at the matter on a per future unit basis. But, the total costs are still pretty stunning, and "a growing trend is to make substantial improvement in aircraft over the two or more decades they are in service. This results in substantial R&D costs, which, makes new aircraft even more expensive."