A few years ago, someone from Argentina posted a lengthy article on conditions after their economic collapse. All of it made sense, but many parts of it had points that most people wouldn't have thought about.
Anyway, his considered opinion was that when law and order break down, you don't see your adversaries coming 200 yards away because there is nothing to identify them. Hence a rifle is not the optimum choice.
Chances of any such event here are pretty slim, I think. So I don't worry about it. But right now, home invasions, burglaries, and attempted muggings happen all the time.
So, FWIW, he recommended a handgun.
If you're stuck on a rifle, a lever action 30-30 will put a lot of lead downrange reasonably quickly. It's not too expensive, it's light, and the carbine length models handle well. A related alternative is the Henry 22 lever action. Shooting Velocitors, it's a fairly potent alternative for $250.
The SKS used to be cheap to buy and cheap to feed. I remember wincing at paying $.20 per round for really good reloadable ammo, when throw-away ammo was $.08. I think those days are gone forever.
For around $450 you can get a Kel-Tec SU-16 A or B. I paid a little more for the C model, and I really like it. I could have easily bought an AR-15 at that price, but for whatever reason, chose the SU-16 and am happy with the decision.
Smith and Wesson makes an M&P AR-15 that sells around here for $600. That sounds like a good choice.
In bolt actions, I recently picked up a Yugo Mauser 8mm for $200. It's a very capable firearm. Once in a while you can get a Finnish Mosin in that price range, and they are better than the Russians. Sadly, the days of getting those for $175 seem to be over as well. But they are fully capable of bringing down a moose at 200 yards.