You can buy a new M-4 or other Auto, but that doesn't explain the costs. I believe it's all in the trigger mec that makes the difference. That's what's the selector switch was for. To selecte Safety, Semi Auto and Full Auto. It's my understanding that brand new rifle can be purchase, so why the cost. I can see it on older rifles before 1986 or so year. I know that the seller of firearms have to have a special lic to sell those type of firearms.