Buy something that has cheap and reliable ammunition, so that you can afford to do a lot of practice shooting.
The effectiveness/safety of a firearm is
90% operator skill
9% not jamming/overheating
1% the rest of the gun
Don't get a short barrel shotgun tho, that will have more spray, and you might end up shooting something you didn't intent to. Also don't discharge a firearm inside your house, statistically speaking you're more likely to wound a friend or family member than anything else. People who break into houses are not trying to challenge you to a dual, they will just fuck off if they see you, and go for a house that's easier to rob instead. And don't point it at somebody unless you decided to shoot. The movies lie, it's not a tool that makes people compliant and do what you demand, people will either freeze, run away or attack you.
I can't tell you anything about what brand or model to buy because i don't know shit about that, but consider buying one second hand from a gun-nut, that's likely even cheaper than a budget-model. Consider it a training rifle, where you find out what matters to you.