The problem is that fighter aircraft have gotten too expensive to afford to build, even for a nation.

Sure, that is a problem. Ironically the best solution from an overall expense management standpoint is to drive economies of scale by building more and retiring older units on an accelerated schedule to cut maintenance costs. Keep production lines running continuously instead of periodically starting and stopping. The F-35A, while badly flawed in certain ways, is at least relatively affordable due to high production volumes.

Not to build, but to build and maintain. We never budget for maintenance (we as in companies and governments).