My advice for someone with only a pistol is to get the shotgun. Diversity and ability to do different tasks is important. Two pistols doesn't further your home defense ability like a pistol and shotgun does. A shotgun is a whole 'nother class of weapon over a pistol.
Every basic collection should have a pistol (for nightstand and/or carry/car carry vs. carjackers, etc.), shotgun (serious home defense/barricade/hunting - birds, rabbits, up to medium game like deer, etc.), and a rifle (depending on the rifle, you can use if for home defense/barricade/SHTF/hunting).
Shotty's are arguably the best home defense gun, and loaded with 00 buckshot will give you immediate fire superiority over all but the most well-armed thug. I have a large assortment of handguns, rifles, and shottys. My go to gun for a serious home defense situation would be a Remington 870 with 00 buckshot - just rack one in the pipe, barricade the door, and call 911. I'd pick that over even .308 rifles, 5.56 rifles, handguns, etc.
And if you watch the classifieds, you'll easily find a Mossy or Remy for $250 or less. I see them about 4 or 5 days a week on classified adds. Both are good, I like and have both. You can't go wrong with either if it's in good shape. And at that price they are a real bargain. Heck, I just read a post that Walmart has the 500's for $200!
Buy a bulk box of 00 and go to the range and pattern your shotty. And get a few boxes of birdshot for the clays and practice a lot.