I don’t know if cheap is way to go with this, low cost yes but cheap has issues, and with this is immediately life threatening.
Would say pay 200 more and get a low range quality firearm or buy a gently used one. Make sure you get range time and understand most houses offer concealment only not like on TV shooting through doorways and Noone shoots through dry wall like it is concrete.
Also with shot gun it is a what happens to missed shots ie what is behind the area you are shooting at, what if it is a sensitive place or has other family members.
I also prefer number 1 buck shot, 00 is 38cal 1 is 32 caliber but you get 2 more pellets with 1. Learn about cut shells, combat loading +practice. Have a defense point that is more than dry wall…. if your house take off drywall and sandbag inside then close up.