I agree with the previous post. An SHTF rifle should always be chambered in common calibers. The best cartridge in the world is useless if you can't find it. My rule of thumb is that if I can't buy ammo for it a Wal-mart, I don't want to own it. Given your (and my needs, since I'm a Florida boy) you are looking for a gun that is reliable, accurate enough at a hundred yards, has hi-cap mags, and frankly looks intimidating enough to persuade the looters to look elsewhere, and will do for hunting in a pinch.
My reccomendations are:
AR-15, you can find them for around $750 or less if you look, cheap mags, affordable but not cheap ammo
AK-47 (my first choice for you) reliable and cheap. Classic arms and k-var are both having huge sales. You can get a converted Russian for $500 at k-var and a Rommanian Wasser for about $400 at Classic arms (both are very reputable companies). The Ak offers dirt cheap ammo, but slightly higher priced mags, $20-$30 vs $15 for an AR. It will also go bang period. You sacrifice some accuracy, but at down the block ranges, who cares.
Kel-Tec SU-2000 This a folding stock pistol caliber carbine that is designed to accept hand gun mags. It comes in 9mm and .40. If you order in say, Glock, it will be interchangeable with your handgun. I prefer a rifle caliber to a pistol caliber carbine, and am not a huge fan of Kel-tec, but lots of folks love these.
M-1 carbine, a classic for a reason and just fine for doing busines three dors down. I would hugely prefer an AR or AK, or even a mini-14, but still a valid choice.
Lever action in .44 mag, 30-30 or .308. Slower, less capacity, but it will do the job and not scare the neighbors.
Good luck
FQ13