You don't tell us HOW MUCH of a budget you are restrained by. For $100 or less it's pretty tight and will limit your choices. A single shot shotgun is a reasonable sub-$100 choice, given training and practice. With a couple of tricks and some practice a single shot can be fired about as fast as a repeater for a couple or three shots. The gun should be equipped with an ejector and the shooter should practice holding an extra shell or two between the fingers of the firing hand. With dexterity and practice the gun can be reloaded pretty quickly and readied to shoot again. As always it is better to depend on hitting what you shoot at than shooting again quickly- old saying is that you cannot miss fast enough to win a fight.
If the budget extends to $200, there are lots of good used repeating shotguns that can be had for less than that amount. Or IMHO the HiPoint carbine is a good sub-$200 choice as well.
Good luck in shopping, and stay safe,