Parker, you're lucky to live in Arizona. You are one of the 17 states that has "puppy lemon laws".
Arizona - Title 44, Chapter 11, Article 17 of the Arizona Revised
Statutes "Pet Dealers" section. Covers contagious or infectious
diseases for 15 days; congenital or hereditary defects are
covered for up to 60 days.
http://www.animallaw.info/statutes/s...1799_01_09.htm
I assume since your puppy is only four months old that you haven't had him very long. The law requires you to get a signed vet's statement about his condition within five days and present it to the person who sold you the dog. I don't know what you paid for him, but the breeder would be responsible for vet bills up to the full amount of his purchase price. It may not cover the entire expense of the surgery, but it sure would help with the costs.
I am so sorry you are going through this, but at least you have some financial recourse even if you didn't get a good health guarantee.