Spike's Tactical sells their complete basic rifles for just about $800. They get good reviews by a lot of users over on AR15.com and have fairly recently disclosed paperwork regarding their "mil-spec"-ness.
Along with Spike's, companies like Daniel Defense and Bravo Company USA are getting much more mention and attention nowadays over the old mainstay brands like RRA, Bushmaster, Colt, and LMT because of their better pricing and options available (things like cold hammer forged barrels, choice of carbine/mid0-length gas, and pre-installed rail systems).
I mention Spike's first because these other companies don't appear to have any offerings within your budget. I'd suggest heading over to www.AR15.com
to do some research if you haven't already.