Do we need a car capable of going 120 MPH? Do we need a TV that receives 1,000 channels? Lots of the things we take for granted today are wants, not needs. I might need one firearm to protect my family, but I own a lot. I also happen to own a number of different machine guns. They're simply a lot of fun to shoot.
The requirements to own a machine gun in the USA are (1) no local city/state prohibition on ownership, (2) application to BATFE to transfer a legally registered gun to yourself, (3) payment of a $200 tax on each transfer, (4) submission of a set of fingerprints, and (5) a letter from your local LEO that you do not intend to use the firearm for other than lawful purposes. That tends to be the snag for a lot of people, but there are legal ways to avoid that letter which don't serve any purpose here. Basically, if you can own a firearm, you can own a machine gun, if you have the money to buy it and feed it.
Actually I recall seeing some figures on state ownership and I believe Texas has the largest number of machine guns. There are I believe seven examiners in BATFE who handle all the transfer applications, and Texas has one examiner assigned to that state alone.
Yes prices have greatly increased lately. It was the Hughes Amendment that passed in 1986 which prohibited the manufacture and transfer to individuals of any newly mnaufactured machine guns. The supply of guns is now fixed, no more can be made, and prices are climbing. Pre 86, I sold a 1943 manufactured .50 M2HB BMG for $800, and today that gun would likely sell for over $30,000. Would that my foresight was as sharp as my hindsight!