Hunting license and a pump shotgun are your quickest and easiest route that you can personally take. As other's have said a family transfer is possible but you seem to think it's unlikely to happen for you.

Pump action shotgun will be reliable and plenty to defend your home with. #4 buck is by far and away the best loads to use in your home if you are worried about penetration of walls and still have enough stopping power to take down a target with a single shot. Shorter barrels are better for inside and don't fooled into thinking pistol grip only shotguns are a good idea you will want to shoulder it.

If you can afford a little more there's some great inertia driven seminauto shotguns in the $500-750 price range. If shotguns aren't your thing you could go with a rifle (handguns are off the table unless you family gifts you one). AR15 and other semi auto rifles can be used for self defense but overpenetration becomes much more of a worry especially if you live in a house with drywall walls and a stucco on the outside. You can get into an AR on the cheap end for a similar price point of a semi auto intetia shotgun but a more realistic number in the current times is $750-1000 for a starter rifle.