Get yourself a pump action shotgun, 12 ga or 20 ga (depending upon your tolerance for the recoil...or kick).
A mossberg or Remington 870 are the two best choices..however, if you are concerned about theft, you might want to opt for the lesser expensive Mossberg. (I have both).
You can get a home defense model, with a stock and 18.5 inch bbl at most stores that sell guns for less than $200. Resist the tempation to get a pistol grip shotgun. The recoil is projected right into the hand holding the grip, and it isn't terribly accurate.
As for the gun laws, I dont know..I THINK such a shotgun, stored in a case is ok in most states. Check www.packing.org for more details.
Your biggest problems would likely be in NY, NJ, Mass and MD...However, you might not be going there anyway.
I don't know.... I've got one, they "look cool"....
aim at the toes......hit 'em in the nose....hahahahahahahaa