If you want a "tactical" 5.56 then you really only have one choice. Get an AR from one of the many respected brands out there that all have plenty to offer with different options well within your price range. RRA, DPMS, Colt, Bushmaster, S&W, Stag,.... IN NO ORDER (lets not start that up).
I prefer carbine length, lightweight government profile barrel, with a flat top for eotech, acog, or scope and BUIS of course.
If you get over the tactical bug then the mini-14 is awesome. I like those like I like an M1A, nothing on it, iron sights. You can dress them up too but in my opinion it looks silly and takes away from what I like about the mini - simplicity, rugerness (read ruggedness) and great irons. Its a ranch rifle people, wood is good!
Saiga's are sweet too, but I like 7.62x39 for my AK variants and have no experience with 223 Saigas, although I would expect they are good too.