If you're handy, you can put one together from parts for closer to $600. For your first AR, buy an Armalite, Bushmaster, Colt, Rock River, Olympic, or DPMS- they all have warranties.

It really depends on what you want- If you want a DCM type rifle or varminter figure on starting at around $1200, if you want a m4 type carbine figure on the high $900s, If you want a plain jane A2 type rifle you'll pay $700-850. Add 300-400 to any of those figures if you want to get a colt.