Cost accounting for a project like that can yield wildly divergent per-unit "costs," depending on how certain items are treated.
Is R&D that led to breakthroughs used in the project expensed elsewhere, or attributed to the project? What about all the time and effort leading up to the prototype?
Is it calculated on the margin (as in, we wouldn't have had this expense at all if we didn't have the F35 program), or do you attribute salaried employees' time to the project, even though you we'd have been paying them if the F35 were done by someone else?
What about contributions to PACs or other "causes" favored by key members of the group that makes the decision?
Or do you circumvent the whole thing, and count only what it would cost to build one more F35, and just ignore all the stuff that led to the ability to do that?
What about any of a hundred similar questions...what actually constitutes a cost attributable to that project?
You can comport with cost accounting principles and come up with God's own number of answers to what would seem to be a simple question. The bigger the project, the bigger the range.
Side note: How do you hire an accountant (especially a cost accountant)? One question: How much is 2 + 2?
For candidates that answer, "4", shake hands, thank them for their time, and show them the door.
Hire the first one that says, "Hmm...could be a lot of things. What do you want it to be?"
