Self defense implies being able to do that in a much larger time frame. It's luck of the draw that you will only be assaulted when you happen to have access to a long arm.
For inexpensive, pick up a Ruger semi auto pistol in .380 or 9mm, shoot it some to be familiar, and get all the training to pass a CCW. Then you will have the big picture covered - a gun ready to hand at a moment's notice all day long.
You can only do that with a rifle in a combat zone, or a backwoods hunting trip. The reality of peaceful life in America is very obvious. Have you seen people walking around with rifles 24/7 in the streets going to work?
Since the rifle will be stored in a gun rack at home or the vehicle 99% of the time you own it, all you need a a capable caliber and reliable action. A lever .30-30 could do that on a $900 budget, leaving plenty of money for the pistol and half a dozen good holsters.
As for the need of using a military grade weapon with 30 round magazine in self defense, if they saw you had it, likely nothing else would. On those rare occasions where they do, less than three shots settles it.
Which means, buy the gun you really like, cause if you don't enjoy what it is, then the money you spent to have one would be like having to buy a hammer. It just sits on the tool bench until you use it and throw it down again. Nobody daydreams about using a hammer for fun during the day.
Setting up some cans or targets at the range and blasting holes in them, yeah.