I prefer to use one of my 22 LR rifles, no scope needed. I also have 22 cal. pistols but they are actually harder to get a good shot with since you need to be fairly close to the animal and that tends to make them turn away. That doesn't happen with the rifle.
You should be able to find one in a pawn shop for little money, even a single shot type will work just fine.
I've seen some in pawn shops for under 50 dollars that would be great hog harvesting rifles.
Buff. In not all the countries it's so easy to own/find a firearm, here in Catalonia (Spain at the moment) is imposible to find a firearm on a pawn shop. I don't have a gun license, but licenses are hard to get, shotgun is the easiest (you can own a 12 caliber shotgun much easier than a 22 rifle, but you still need to do a psychological exam and justify that you own a hunting license, and have an interview with the police)... A handgun is almost imposible, you have to be a member of the police or have your life treatened in order to be able to legally own a handgun. That's the reason that I was asking for those calibers. I was wondering the 20 shotgun with birdshot... If the moment arrive, maybe I give it a try before with a piece of meat with bones, and I feed it to the dogs. Many thanks for he answer, though.
Your best bet in that case is to give it some really tasty food and using a very sharp, long knife, stick it under the jowl and cut the carotid artery to bleed it out quickly. Once you stick it you will want to move away a little so the hooves don't get you.