Just how difficult is it to manufacture automatic weaponry from scratch?

[ersoz]

The question should have been, how expensive is it to manufacture your own automatic weapon. Or even creating a production line...
In certain regions of the world, it is possible to purchase automatic assault rifles for less than 400 US dollars per unit. Why bother manufacturing your own if they are already so inexpensive?
Manufacturing "something" is not extremely difficult. If you have all the equipment/machinery which will most definitely cost millions of dollars. I'm talking about creating moldings and serious metalworking.
Also, I don't believe the Kalashnikov AK-47 is the most "illegally" manufactured weapon in the world. But it sure is the best known.
Slightly off topic perhaps but I'd like to share this trivia with you from the movie Lord of War. Instead of using prop AK's for a particular scene the production crew decided to rent real weapons from an armsdealer.. It just cost a lot less.