Good for you. It's overwhelming at first but you can totally do this within your budget and i would say that you can put glass on that rifle and still be under that $.
I bought a stripped lower. Mil Spec. (very important for ease of building)
I then bought a Rock River 2 stage match trigger. It's great and a good value. I bought a grip that is comfortable, and with an eye on weight bought the other parts like the adjustable stock and others. You can literally go to Rock River or Midway and get a complete parts kit for the lower, and get the standard things and replace with the upgrades for the parts that you want.
I spent the extra on the trigger and grip.
I then got the Midway M4 feed ramp chrome lined barrel in 16" and 1:9 twist. It was under $300 and loves the factory Hornady 53s so much that i haven't even bothered to work up a hand load yet. (based on the 5 shot group below, i have other things that demand my time more)
I guess the simple answer is buy a stripped lower, get a parts list, and buy those things and upgrade the things that are important to you. Midway has a video that makes it stupid simple to do. Then buy a complete and assembled upper. You can get into doing that on your own later, but would advise staying away from upper assembly until you have a lot more knowledge. It's where people get into trouble and have problems.