I'd be willing to bet that most of those machine guns, if not post samples, were bought a long long time ago when the prices were much much cheaper. Back in the 70's my father had a chance to buy a thompson m1a1 from MGM for next to nothing and I know of several people who own uber expensive machine guns that they bought when they were in there early 20's but now they have a hard time setting back $500 for a pistol.
The higher than usual prices clearly show those are just there to be looked at, he has no real want or need to sell those machine guns.
I'd just about bet theres a good deal of post samples in there, IF that minigun is transferable they run over $200k and up. Parts kits and garwood 80% recievers are much cheaper if you catch my drift.
Funny thing about a DIAS, a coworker has one....his mother bought his father one before they got married in the 80's out of some mag. There 100% clueless that it was illegal, nor do they care.