I would really recommend a Mil/Mil scope. It has made my life considerable easier. In your price range look at the Vortex PST or The Weaver Tactical. Stay away from Boone & Crockett or BDC reticles (they dont work for a damn for LR) look for Mil-Dot or Mil-Hash reticles.

But to be 100% honest with you buy offgrid's NF and be done with it. He let me shoot it and its perfect.

http://www.ar-15.co/forums/showthread.php?t=68535

Just tell him I sent you!