fighter unit cost hypothetical question

the typical DOD acquisition process of fielding
a new fighter platform involves the bean counters
adding up per unit cost.

now we all know from basic economics theory, the
more quantity we produce, the efficiencies of mass
production kicks in, and unit cost should go down.

this might be an "out-of-the-box" idea, but "what
if" - say Boeing, were to reopen the production line
of the F-18, and sell a non weaponized version of it
to affluent civilian customers ? (with of course
very strict legal constraints, and perhaps a monitoring
system to verify it doesn't get into the wrong hands -
ie. Cuba, or Iran, etc).

actually it doesn't even have to be an F-18, let's
say it's an F-35 - build a ton of 'em and sell 'em
to any US citizen (preferably after thorough vetting
process) who has the money and desire to buy one.

of course, FAA certification/flight training/ and
insurance i suppose is another matter entirely. but
i would suspect it would be along the lines of the
folks who would buy old T-38 Talons.

does anyone know if a US citizen can legally buy a
Mig-31 from the Soviets ?? they sell to anyone who
has the cash don't they ?