OK, from the sounds of the original post, SHTF, "homeland defense" and home defense and carry are also mentioned, it sounds like you are looking for a good overall "practical" use (as opposed to fun at the range) "arsenal" on a budget.
Pick one of these options from each catagory as funds allow (start with the concealable handgun if in a carry state, start with the long gun if not), then when/if funds allow more pick up a second from each for more versatility:
Long guns:
-12 ga pump shotgun. Yes, recoil can be brutal, especially to a non-shooter. However, they are great HD guns, and versatile in a "SHTF" situation (whether Katrina-like where you need a good HD gun, or total collapse where hunting for food as well as defense is needed). In addition to being one of the best HD guns, if you are a hunter (or if the SHTF in a total societal collapse) you can hunt everything from the smallest birds to the largest game with simple changes in your ammo selection. New you can still get a good Mossy or Rem for the $200-250 range, and used you can be under $200.
-SKS. Cheap, cheap ammo, more range than the shotgun, and still good for hunting deer sized game.
-Hi-Point Carbine. I had one that was a very reliable gun. Even though 9mm and .40S&W don't improve much with a carbine length barrel, you still have practical accuracy advantages over a handgun. Ammo is cheap and you can carry a lot of it if you need to. They are still under $200 new.
-30-30 lever gun. Can be topped off between shots, can be fired very quickly, decent power. A bit much for home defense in a populated area, but if you are in the country they are usable for HD and they are great for hunting deer sized game. Can still be found in the $250-300 range new, and great deals are available used.
-.357mag or .44mag lever gun. Most of the advantages of the 30-30 lever, you can carry more ammo and ammo is much cheaper, it is more suitable for home defense in a suburban or urban environment. The only disadvantage v. a 30-30 is cost (used you may find one around $300 or a tad less).
-.22lr semi-auto. Sure, it isn't the best defensive gun, but in a long gun it is acceptable. Cheap ammo means cheap practice (if you are poor ammo cost may mean more to you than the cost of the gun) which means more practice.
-.22mag semi-auto. Still cheaper than just about any centerfire and more "oomph" than a .22lr.
Concealable handguns:
-A used 3-4" barrelled K-frame .38 or .357. An OK size for carry, simple to use, reliable, accurate, and very versatile (especially the .357mag). .38spl practice ammo is relatively inexpensive, and both calibers are extremely easy to learn to reload for to save even more money. You can find the .38s in the $200 range used, $300 for a new Taurus 82. You can find the .357s starting in the $250 range used, $300-350 new for the Taurus 65.
-A used 2" S&W J-frame or Taurus 85. Much more concealable than the K-frame, most of the same advantages (though it is much harder to learn to shoot well). The Taurus may even be doable new at the $250-300 range new.
-Taurus Milennium series. Well under $400 (usually under $350), reliable, accurate, and in good defensive calibers (9mm, .40S&W and .45ACP).
-Ruger P-series. Not so concealable, but the polymer are doable. Decent prices. Extremely durable and reliable.
-Taurus PT911 or PT940. Decent prices, fairly concealable, reliable, full-size gun capacities (15 in 9mm, 10 in .40).
-CZ. The 75B is concealable for some people. The Compact is for most. The polymer 100B is concealable for most. Prices are still reasonable, but going up.
-Bersa .380. Very concealable, reliable, pretty accurate, quite affordable (still under $250 new in most locations).
Reloading gear:
-Get a cheap Lee press and basic kit and you can make ammo for far less than you would have to pay to buy it. If you are poor this is a must have, it will pay for itself in only a few range sessions.