That PSA $500 rifle kit Purehavoc linked is a great deal if you want an M4 profile barrel (read Primer about barrels). You'd just add a stripped lower. Remember that a $100 lower locally and a $75 lower plus $25 transfer fee cost the same but in a free state you can have the local one the same day.
Anyway if you miss this deal there will be something else good coming down the pike. And again, get up to speed on barrel profiles. Many of us prefer midlength gas over carbine length gas. And the lightweight profile over M4 (medium) or M4A1 (heavy).
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek