The one your going to build ...... A $1000 wont get you much if your buying one new from the factory. About the only one I can think of is Double Star, they run anywhere from $650-$800. But, have you thought of building one? You CAN get a complete lower from RRA or Stag for like $215-$235, or you could build your own for a little less(depending on what you want). You should be able to pick up a new upper(without rails, rear sights, bolt, bolt carrier, and charging handle) for around $300-$350. Look at http://www.eaglefirearms.net, that should give you a good idea on decent prices.
Edit.... I was looking in a 2005 Gun Buyer's Guide at the AR's they had listed. DPMS and Double Star were the only two companys that listed AR's for less than $800. All the rest were like $865 and up for the suggested retail. The only thing I dont like about Double Star is they have cheap lower parts kits. But their stripped lowers and uppers are very very nice for the money.
Complete Stag lower with 6 position stock = $215 before taxes, shipping, and transfer fee.
Complete Double Star 16" or 20" upper w/ bolt, bolt carrier, and charging handle = $399.99 before shipping/taxes
For $700 you could have a complete rifle with either a red-dot, iron sights, or a scope. That would leave you $300 for mags/ammo and stuff like that. Or for quality flip up rear sights and a decent red-dot. Hope this helps.
For $1000 you can get an AR made by a top manufacturer, ie Bushmaster, Armalite, and such. For that price, you can also get some models in 308, including the DPMS and Eagle Arms (by Armalite) offerings.
Question is what you want in it. You could get a decent service match rifle, a many rail equipped carbine, a bull barreled rifle or carbine, or one of many other options. You could buy a $700 AR and put a $300 stock on it. You might possibly be able to get one of the new piston driven models, or have a standard AR converted for them.
So what is it that you want?
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Well, I've given some more thought to what I want, and see as how your interested in AR's, I might as well post it here. I bought a Double Star stripped lower for $100. I'm thinking about now going with a Del-Ton kit, as I've heard nothing but good things about them. For $495 I can get a complete kit(everything I need to finish my rifle minus a rear sight). Thats a 20" upper with a different flash hider(and a green handguard), lower parts kit, 6 position stock(green), bolt/bolt carrier/charging handle, everything. So that puts me to $595, say $100 for a red-dot, so $695, than stuff like mags, a sling. So I should be able to build myself a nice rifle, with all new parts, for $750. And I'll know how it all goes together too. One thing I've learned, AR's arn't that expensive, its all those freakin addons you want later.
I've heard some good things about Model-1 kits. It is cheaper to build one than to buy a complete rifle. Bushmaster just went up about $100 in the last month. I saw one at the local gunshop for around $830 or so last December, I looked at it yesterday and it was now $927!!! I asked the owner and he said that everything is going up this year around 8 - 10%.
Olympic arms make pretty good stuff. With the popularity of the AR-15 family at an all time high, some of your smaller companies have had to step up their quality control with Rock River leading the charge. It is actually cheaper to build an AR-15, than to buy a complete rifle. I've been flirting with the idea of building one from scratch from a stripped Bushmaster receiver. There is an abundance of manufacturers out there that can proivde whatever parts you need, also keep in mind, whatever manufacturer you go with, all of the parts are interchangable.
What is the best AR-15 for $1000??? 
...... A $1000 wont get you much if your buying one new from the factory. About the only one I can think of is Double Star, they run anywhere from $650-$800. But, have you thought of building one? You CAN get a complete lower from RRA or Stag for like $215-$235, or you could build your own for a little less(depending on what you want). You should be able to pick up a new upper(without rails, rear sights, bolt, bolt carrier, and charging handle) for around $300-$350. Look at 
