Suggestion:
Get the lower first . . . legally speaking, that's the gun. If there were to be a ban, that would likely be the first restricted item. Spend 250-400 or so on a really nice complete lower with a decent trigger, like a Rock River Arms. Take the left over 400-500 or so dollars and get a decent barrel and complete bolt carrier group on order, The rest you can put together with very little money. Of course the sky's the limit but you can always upgrade stuff later. My Stainless Bushy barrel came with the handguards, gas pipe and front sight. Except for the upper receiver, there's not much more to it. Good luck.
I put a DPMS together the way I described and it's perfect. Shoots way under and inch at 100yds.