Also, on average, how much do they cost?
As long as you know what you are getting into and have the room and ability to train a 150lb pig, this site should be able to help you.
There’s a section for breeders and rescue. I have no idea how much they cost from a breeder as I only ever see them coming through my rescue lists when people realize they don’t stay tiny and cute. A good breeder will spend the time to get to know you before selling you a pig so be on the lookout for those just wanting to make a quick buck.
I would recommend checking if there are any local or state laws that would prohibit you from keeping a pot-bellied pig. All I was able to determine is that the Illinois Department of Agriculture considers them pets and not livestock (if they were livestock, your property would have to be zoned agricultural to keep them). But there may still be local laws against pot-bellied pigs; I found an article about someone in Hinsdale, IL who lost a court battle to keep two pigs. Both laws concerning livestock and those concerning exotic pets might apply.
Since pot-bellied pigs are exotic pets, you need to make sure you choose a reputable breeder who has extensive experience with these animals. It would be more expensive than buying a pig from a ‘pig mill’ but it will help ensure that the animal is not sick or abused. (This goes for any pet, of course.) Finally, as with any pet, you need to be sure you can take care of it. Exotic pets especially tend to be really cute when they’re babies, but in less than a year you’ll end up with a 125-150 lb pig that could live 12 to 15 years. This is about the same as a very large dog, except with much greater demands on diet and living accomodations.