with the requirments you laid out in your post your are pretty much tying yourself into one of the better AR15 platforms. No knock there, they work fine for me. Forget the circa 1960's arguments about dirt build up, jamming, not reliable, bla bla bla
todays AR15's are very fine weapons.
If you were not adverse to the 7.62x39 cartridge I would look at one of the AK47 clones as well, but the AR15's from Bushmaster, Rock River, Armalite, Stag, etc are good stuff, and can generally be found in the $800-$1500 dollar range.

Someone posted a Kel-tec (you were kidding right) This is your life you are trying to defend here isn't it?