Inexpensive Punch
Having reviewed the request and all the suggestions, I'll chuck a couple of pfennigs into the mix.
Saiga. Recommend .223/5.56 as the ammo is more widely available and commercially made in the U.S. at reasonable prices if you shop carefully. The un-converted Saiga rifle is legal just about everywhere. You'll need to get spare mags, as they're not a cash-and-carry item in most towns. You can usually get one for under $300 (I recently found a supplier who can get them locally for $260). Ballistics adequate for most uses. Sux for bigger game, but fine for car doors and vests.
The
.30-30 carbines can usually be had for around $300. Shoots through schools. If you need more range than 150 yards, use Horandy's LeverEvolution ammo. It's 160 gr, spitzer style tip (plastic), and flies true out to 250 yards.
I would normally recommend the
Marlin 1894C in .357 magnum, but prices have gone up and they're now typically over $400 -- unless you can find the Big 5 deals where they drop them to $350. Try also Walmart special order, which may be around the same price. Doesn't shoot through schools, but certainly through car doors.
I have the
Kel-tec SU-16A. It eats everything, including generic gun show bag-o-bullets. Unhappily, it's just over your price requirement. Good rifle, though.
Likewise the
M1 Carbine. Except that I'd hate to lose one in a car theft. I'd get all emotional and stuff.
Too bad about the "no pistol calibre carbines" thing. There are some nice and inexpensive ones out there.
If you can stretch a little, the
Kel-tec would be just about ideal, meeting all but the "price" requirement.
Failing that, an unconverted
Saiga (.223/5.56) meets all your requirements except "standard magazines" so you'd have to buy some spares in advance.
For what it's worth, we will be buying a matching set of Saigas for our family (4x 'cuz there's 4x of us).
Afterwards, when we're rich and famous (*smirk*) we'll upgrade to something a little more American.