Well after checking some prices, for the most part either DPMS or RRA will start around a grand.....depending on the model. My opinion, for what it is worth, you might as well kick in the other 400 and get an AR-10..just my opinion.
I did find a red dot site that does not use batteries, but it is in the 650 to 700 range...
www.kimberamerica.com/shop/product.php?xProd=9&xSec=14
I have to say also, that we have had the discussion about the AR-10 for home defense, it is not a CQB weapon, even the way I have mine configured, but it is more suited for what I call CRE (close range engagement). My self at this time also have a 12 ga and a .45 for home defense, going to get a M-15 hopefully this spring....If the bad guys pull up in front of the house, well the AR-10 will have no problem filling the vehicle full of nasty holes....
But in the house, well I don't want to put a bullet into the neighbor's living room....would not be good
I am not trying to deter you in anyway, just giving you some honest input.....and just in case you are wondering....I have almost 4K in mine...hope any of this helps....when you decide on a price that you are willing to spend, the fun will begin.
Base rifle.....$1000 to 1500.00
Sights......$200 approx if you go with a A4 type of rifle.
and then you have optics and a hand-guard (optional)
and a few other things depending on what and how you want to build it....
If you want I can compile a list of prices according to what you want....
BMS