For my money you are getting a sub-par round in a platform designed for accuracy.
Inside 300 yards the 7.62 x 39 is deadly. Beyond that it has the ballistics of a flying aircraft carrier.
The AR platform in it's DI configuration is designed to be a more accurate rifle system than Uncle Mihkail's piston driven eastern bloc offering.
So with a 7.62 x 39mm AR-15 you are paying for accuracy that you aren't getting. In my mind anyways.
Now if you got an AK, it would be a lot cheaper and you would have the heavier short range bullet option.
If you want to take advantage of the AR platform, I would look at a wildcat like the 6.5 Grendel or something like that where you can still pack a whallop, but get distance out of the round as well.
Just my $0.02 - YMMV