Thank you for adding the additional information regarding how hard these weapons are to obtain.

To add to what you've said, it takes more than just a permit to get many of these weapons.

Any automatic weapons created after 1986 requires you to become an FFL ( a licensed gun dealer) or firearm manufacturer. Both of these are significant business endeavors. While an FFL can be slightly less involved, you can only own a "sample" of a post '86 automatic firearm that can be used for police department testing.

Source

The weapon in this picture appears to be a M134 Minigun mounted on a remote controlled turret.

https://en.wikipedia.org/wiki/Minigun

The M134 is a significant amount of firepower.

There are M134's are (very) rarely in circulation but can be bought by regular citizens. With that said, they are incredibly expensive. Not "get an extra day job" expensive but "Mad scientist with an evil lair" expensive .

This one is currently on sale for $285,000. If the product page is to be believed, there are about 12 of these currently in circulation in the US.

The gun has an adjustable firing rate. Assuming it's set at 4000 RPM firing it for 3 seconds costs ~$93.6 dollars (that's assuming it can use regular .308 instead of the 7.62mm)

Here is a video for extra funsies