In general, if a pershas no guns, I recommend:
1. Get a cheap, reliable, used revolver in .38 special. $200 + $50 ammo. Learn to shoot with it.
2. Get a cheap, reliable, 12 gauge 5 shot (5+1) pump. If you look, a very good Turkish made Tristar Cobra Force is 7nder $200, NEW. +75 ammo
3. Get a cheap, reliable AR in .223 Wylde. $500 + $100 ammo.
Practice, practice, practice.
A revolver is a good first choice and may be easier to practice with.
Having an AR-10, AR-12, AR-15, etc. works depending on the house layout but may be a lesser choice if you can't get enough practice with it. One problem with a long arm is that you may not want your neighbors to see you transporting it to and from a range whereas a handgun is much easier to avoid detection.