What it really boils down to is you.
What do you want? What do you want to do with it? Do you want a plinker, a tack driver, or something in between?
On the cheap, DPMS makes a plinker model for around 700 bucks.
For my Bushmaster A2 Target model I paid $922 out the door, but for the M4 style I would have spent 500 bucks more.
If you're leaning towards quality, all AR's are superb across all of the manufacturers. For a long time DPMS had a really bad rep, but they've fixed those issues and make a quality gun now. I've personally shot DPMS, Rock River, Colts (in the Marine Corps), Bushmaster, and Olympic. All of these are fantastic.
If you're looking for a varmint gun/tack driver, all of the above can and do make them, as do Les Baer, Stag, and all the other manufacturers. This is where you'll see the increase in price start to shoot upwards quickly simply due to paying for the better fit, better barrel (match grade, free floated, etc.), match grade trigger, and the optional bipod and optics.
If you want a decent all-around weapon and don't want to spend alot of money, look for the A2 or A3 HBAR (heavy barrel) from Rock River Arms. The A2 comes with iron sights like the M16-A2, and the A3 has the Pictinny rail. You can at that point swap out the stock for a collapsable one and add both optics and a bipod later on.
I would recommend for your first AR to get a Rock River for the lifetime warranty.
The M4 versions generally will cost more than the full length, so if that's the route you want to go just keep that in mind (and it takes some of the money away from good optics if your limit is 2 grand).
Kris