The most reasonably priced is probably a used police pump action 12 gauge. If your wife is going to use it stay away from a pistol grip. The pump gun makes a noise when racked that circumvents all languages. You might want to load the first round to be cycled with a non lethal round. The rest 00 buck. The purpose of the non lethal first is obvious. Most good people hesitate to take a life and then there is friendly fire when your sneaking in late. A rubber bullet will just make them wish they were dead.

mossberg pump home defense gun, holds 8 rounds and is an easy shooter at a good price.

you can shoot someone from 10 feet with a 410 and their plans will change or end rather quickly! just something about it hitting them in the face or chest plus the boom in the dark will make them run or just fall! think about if it was you who was shot! a 410 has almost no recoil, but in the dark with sudden noise and a serious wound to the face or just no face at all your problem might just be solved. just make sure to practice with the family until they are comfortable with it. in the winter i would go with something more powerful. folks wear heavier clothes at that time.

Two things to take seriously. First and foremost, whatever you decide to buy, make sure you spend significant time familiarizing yourself with the weapon and that includes your wife. This means also talking through scenarios, identifying targets beforehand, and only pulling the trigger when you are certain of the target. Second, look at the layout of your home to help determine your weapon needs. Long hallways and big open rooms would be conducive to a shotgun. But tight spaces and small areas might be better suited for a pistol. Bond Arms out of Texas makes a nifty derringer style pistol that can shoot both .45 long and .410, both of which would do the job in close quarters.

If your wife will be using the gun as well, it may be a good idea to get a gun with an adjustable stock. These can be purchased aftermarket, I believe Blackhawk makes one with a recoil reducer as well. A youth model would also work. I would stick with a 12 or 20 gauge pump like a Remington 870 or a Mossberg 500 or 590. As for shot size, I would use #4s as they will be less likely to over-penetrate than buckshot or slugs. Something to consider with family members and or neighbors just a few layers of wallboard away. At typical home defense ranges, a shot load will be all together, and will impact as one solid mass, spreading out as it penetrates, so as far as effectiveness, shot size isn't as critical as one might think. Capacity is less of a concern than barrel length. Shorter barrels are easier to maneuver in tight spaces like hallways and stairs, and are also harder for an assailant to grab and take away. A flashlight attachment might not be a bad thing either. You can't hit what you can't see, and you definitely need to identify your target.