Lots of options, Aero Precision blemished lowers were $85 last time I bought one, maybe June or July this year, and I still can't find a blemish on any of the 5-6 I have bought in all. Barreled uppers from many sources, I have used redxarms, and a good lower parts kit- PK, DPMS, many others can be found, and typically an adjustable butt stock. Pretty easy to put a rifle together for $700 or so, add some $ for iron sights or a scope & rings and you'll be shooting in no time.
I bought no special tools other than a castle nut wrench to hold the butt stock tight. A hammer, a good nail set, a piece of carboard from a thin box to protect the lower receiver's finish while tapping in roll pins, and tough fingertips to hold springs and detent pins in place are all you really need. The toughest spring and pin to get in is the pivot pin IMHO. What I do is put the pivot pin in place from the back side, but backed out just a hair from the hole where the spring and pin go in. Insert the spring, push in the detent pin(might feel like the pin is going to go through you finger tip), and once the pin is part way in, push the pivot pin in from the opposite side, binding the pin and spring in place. From there, I work the pin down and hold it with a knife blade, pull the pin out and insert it from the correct side over the top of the blade. The taper of the blade will allow you to do this. Also, I grease the trigger pin and hammer pin, grease the pivot and takedown pin slots, safety, and bcg, and light oil on the rest.
The first lower I put together took probably 25 minutes. Second one, the spring I described above was difficult to control and I shot it all over the house half a dozen times before giving up for a night. Wear your glasses or safety glasses, the pin and spring get moving pretty good. Went back at it a day later and finished it. Total time on that one, 2.5 hours. After that, 30 min tops.
You can find pictures, instructions and videos online. You don't need to get fancy, its easy to put together a reasonably priced gun that you can enjoy shooting.
One I shoot has a redxarms A3 flat top 16" barreled upper, Aero Precision lower, PK lower parts kit, and UTG Pro butt stock. With a pursiut X1 red/green dot scope, maybe have $800 into it.
