Have you shot an AR? Go do that and you'll be hooked. Everyone needs an AR and an AK in the armory!
I put my two ARs together, actually assembled the stripped lowers and bought complete uppers. Your price range will get you a great rifle. DI over piston is a smart choice but there are many other specs to consider and you have to decide on them depending on what you want the rifle to do. BCM, Colt and Daniel Defense are excellent choices. Think B,C,D!