At the intersection of firearms law and Microeconomics...
Just saw a fully transferable, National Firearms Act (or "NFA item") M1A1 Thompson submachine gun show up in some local online classifieds. To purchase, it requires a virtual mound of paperwork, fees, etc, but that is small potatoes compared to the asking price: $18,000 USD.
For those who aren't aware, in 1986, part of the passage of the Firearm Owners Protection Act included an amendment barring the sale of newly manufactured automatic weapons; in essence, after 1986 no new automatic weapons could be registered for private civilian ownership.
Predictably, what happened at that point was essentially a cap on the *supply* of legally registered full-auto weapons in US civilian hands. Since *demand* for said items did not decrease, there was an inevitable upward pressure on prices of legal weapons.
A supply that is low and dwindling (presumably some number of guns break or are destroyed every year), plus a demand that is high and increasing equals $18,000 USD for an item that in 1944 cost the US Government $45. In 2019 dollars, that would be approximately $650 depending on how you calculate inflation.