Possibly the best single firearm for the farm is a shotgun. The pump type is likely the best of those as it is is simple, inexpensive and has interchangeable barrels. Mine, a Mossberg 500 has a 26" barrel with a PolyChoke*, a 26" field barrel, a 24" rifled barrel for slug/sabot shooting and an 18" defense barrel. Some I got used, some I bought new. I dont believe I have over $300 in all of it.
* A shotgun barrel "choke" is a taper in the end of the barrel, which reduces shot pattern dispersal. They range from full choke to wide open. The PolyChoke is an aftermarket item fitted to the barrels end and allows for adjustment throughout the range. Most often seen are screw in choke tubes fited to the end of a single barrel, which give the same result.
Anytime you have a gun question, feel free to ask.
I am a licensed collector, a former gun dealer, hunter, reloader, concealed carry permittee and was awarded EXPERT class marksman in military service.
Ill do all I can to help.