Ronald Reagan and Tip O'neil guaranteed that when they passed the 1986
firearms act, in fact raising the price of all Class III firearms. The
act froze the NFA machine gun registry at the number that were
currently registered and transferrable M-14s were fairly rare anyway
at that time. The reason why they were not overly expensive in the
early 80s was it was assumed the millions the US had here and
transferred to governments abroad would eventually work themselves
back here into the civilian market. That can't happen now because if
it isn't in the registry, it isn't going to be in the registry.
The ironic thing is in the same time frame (86 to present) the number
of NFA34 firearms in the hands of exempt police departments and
paramilitary agencies has exploded. It is possible that the average
beat cop might have a machine gun in his car and all of the special
weapons teams have them. The old standard of a cop in a uniform with a
pistol and maybe a shotgun has been replaced by masked men in combat
gear, carrying full auto assault rifles and submachine guns.
That doesn't mean they have the discipline to use them properly. Anyone
can stick the barrel of a machine gun around the corner of a building
and empty the magazine in a couple of seconds.