You can go with an Aimpoint PRO for around $400, it comes with its own QD mount, though I replaced mine with an American Defense mount.
If you want to go a magnified route there are the Burris AR332 and the AR536 optics, at around the same price point, good optics, not going to take the abuse of the Aimpoint but as long as you aren't bouncing your rifle on concrete on a regular basis it wouldn't be a problem.