First,goto AR15.com and learn more than you ever wanted to know about AR’s. Then seriously consider building your own. It is not that hard. And, it’s a good way to get a very affordable one that you have a real stake in. I got a lot of my parts fron delton.com. They are good people.
I highly agree with this.
I built an AR based on the info on ar15.com, saved at least a couple hundred dollars & I know my rifle.
My AR started with a Rock River LAR-15 stripped lower and finished it off with a M&A Parts kit - A4 flat-top w/flip-up rear sight, in a M-4 configuration. Chrome lined barrel, chambered in 5.56.
Building your own gets you what you want, whether it's fully dressed or just the base to start with.
I had never built a firearm before, only had to buy a couple tools in order to do it. Only took an hour or so to put it all together.