Shooting off 30 rounds through a cheap gun isn’t that pricey. Full autos are usually at least $10k. I think you can find something like a STEN or other cheaply made ones for ~$5k.
But yes, some people have mixed up priorities. For some its guns, others its Playstation games, and others its booze or drugs.
Carrying an M134 and ammo like that is pretty silly. But that is the sort of film where such things happen. There is, however, a microgun available now.
According to Wikipedia the STEN cost only 15 shillings to make in the 40s. How can it be USD 5 k now? According to measuringworth 15s in1943 is equivalent to less than GBP 150 now. Sounds like someone is making a substantial profit.
There are fewer of them now, and only a small percentage of those are “transferable”, or legal to sell. Here is one for sale: http://www.gunbroker.com/item/674719069
But they are crappy guns. Here is a homemade one: https://homemadeguns.wordpress.com/2016/09/28/homemade-sten-type-smg-seized-in-brazil/
If someone is planning a crime with a machine gun, they are probably going to find that it is a lot easier to smuggle or manufacture one than to go through the tedious, expensive, and time consuming process to be approved to buy one. 5K is really on the low end for class 3 guns. The more collectable ones are more in the range of 30 to 100K and up.
But back to the stupid glove. I had not noticed when I watched the vid the first time that the guy shooting the AR was using a .22. ( good catch mister44) ,That was why he could sort of hold the gun on target. Also, he has a big battery pack on his belt, and wires running everywhere. Like a suicide bomber.
Oh for sure, if we made more NOW, they would be a pretty affordable gun. They were massed produced in WWII and the design was made for it to be cheap and dirty with primitive machine tools by comparison.
The problem is they are full auto only, so only a limited number were imported here. I bet you can dig up adverts for them for something like $20 in the 50s. But they would also require a $200 tax stamp, which back then was a whole lot of money. So while there were collectors and hobbyist who had them, they were pretty rare - as were all full auto guns.
Then in 1986 the Democrats put in a poison pill in a gun bill and it got passed anyway. So that closed the NFA (1934 National Firearms Act) registry for full autos. Except in limited cases where found guns were grandfathered in, you couldn’t ADD a new gun to the registry, which means there is a set number of legal full autos out there. Thus the price on them has skyrocketed. I am guessing on the price. When I looked into it like 10+ years ago, the STEN was about as cheap as you cold go and it was over $3K. I am guessing $5k is probably the cheapest you can find. Looking around the craptastic Mac 10 is over $7K. Something like an M16 is between $18-$30K easily. These are more ore less identical to a $500 AR 15 in parts, other than an extra pin in the receiver, possibly some more metal removed from the receiver, and some different trigger parts. The price is totally from artificial scarcity.
There are a few other ways to possess full autos. Get a class III dealers license and you can buy what ever. You can buy post 1986 machine guns as “dealer samples”. These can only be bought and sold among other licensed dealers, but they are significantly cheaper. I found some STENS for $1.5K.
The third was is to get a class III manufacturers license. You can make pretty much what ever you want then. You could take a vintage STEN parts kit for ~$150, make your own receiver and a few parts, and there you go. Of course your ability to SELL it is very limited to class III dealers, law enforcement, the military, and a few other select orgs that have the proper paperwork.
Fun fact - most of the gun in the first Star Wars were based on the British Sterling machine gun. The Stormtrooper and Rebel troopers both used real Sterlings that were were converted to fire blanks. Remember much of it was filmed in the UK, and the prop department had a plethora of old Sterlings to use.