And let's not kid ourselves--a skilled shooter armed with "budget" firearms is still most certainly a deadly foe.
As an exercise, let's put together a decent set of firearms for general TEOTWAWKI survival purposes, on a budget of $700. This is just for guns--ammo and support equipment will be purchased separately, however, their cost should be a consideration. If that was your budget, what would you choose?
The SKS used to be the "go-to" budget survival arm; a semi-auto rifle for under $200! Unfortunately, the market price for the SKS has crept up to about $300; still a decent deal, though. The Mosin Nagant rifle is the first that comes to mind when I think of "budget" survival arms--under $100, powerful cartridge and makes a good war club when empty. You can find used Marlin .30-30s for under $300 if you shop around a bit. WASR-10 AK-47s used to be around for less than $400, but the guns I'm seeing now are all around $450-$600. For around $400, you get into some of the cool surplus guns like the Suomi 9mm and the Sterling.
Pump action shotguns are a huge draw when you're on a budget. For $175-$300, you can get a capable 12-gauge that will work well for home defense and hunting. Even the cheap-o single shots, usually around $100, are compelling for survival work.
Handgun-wise, there are numerous options. There are several European surplus guns in 9x18mm that are out there today at around $250. Bersa .380s are out there in the $250 range and get good reviews; most of Kel-Tec's pocket guns and the Ruger LCP register in around there, too. The High Point 9mm is uuugly but cheap and supposedly rugged. Police surplus revolvers--usually Smith & Wessons--are often out there for under $300; new Charters Arms, Rossi and other brands are available in that ballpark. The tank-like Ruger P95 can also be found for around $300.
Or, for the price range we're at, you could go with one quality gun and maybe something else. You could certainly get into a Glock and a pump action shotgun for $700, and you'd be pretty well equipped. Or you could just buy an AR or an AK and be done with it; a good rifle will get a lot done for you. If you look at pictures of soldiers in Afghanistan and Iraq, a lot of the guys don't carry a sidearm--just their carbine.
Anyways, what would you guys do? What would you pick?