You can't build an A3 flattop as inexpensively as you can buy one. But they are better than a carry handle, simply because you can add an optic. Consider that they are military standard on combat firearms these days, irons are no longer minimum standard - just a backup. Bolt guns went that way twenty years ago.
If it's just a paper plinker, any will do. And as said, HD is better served with other firearms.
So - aside from paper - what ranges and targets will it be used for? Spec your features to support that. Will you use this for hunting at all? Caliber and mag capacity are about the only things that could be affected there.
I'll go out on a limb and spec a generally useful recipe: A3 flattop, 16" barrel, midlength gas. If ammo costs are important due to high consumption, stick to 5.56. All the alternate calibers have a negative - either commercially priced ammo costs, or in the case of 7.62x39, not being optimal for the straight mag feed.
Furniture really adds nothing to accuracy unless the barrel is already shooting under 1MOA - which means an A3 flattop with expensive scope.
Which goes back to what range, what target. "Plinking paper" doesn't cover it well enough, simply because there is a huge difference between 50 yards at the dump and 600 yards at a Match.
If just having an AR is the only reason, then $750 and the roll mark that impresses you the most is all that's important. Any one of half a dozen at that price will do the job. Avoid Brandinista rants, simply because that's what they are.