What would be the point? Say the others are sick, what would you expect to then happen? The time to deal with this was when the pup first got sick. You could have called and asked for your $50 back (prob just what you would get in small claims court, the value of the dog) but you would have given back the dog. You could have decided to put him down (as sad as that thought is, that's what many people did back in the late 70's, early 80's when parvo first exploded), rather than incur the vet bill (and we never had to report cases of parvo, no idea who we would have reported them to, or why).
As for bargaining with the vet, because the bill was over the estimate. That's why it's called an estimate..your vet wouldn't know how your pup would react, so all he could do was guess. You could have said, ok, I have $2000..that's my limit. Once you hit that, we need to bring him home.
I'm sorry you are going through this. I wish your pup didn't go through this. I don't think I'll ever forget the smell of parvo. It got so we could tell a dog had it when brought in by the smell. It's a horrible disease. But you had choices, and I don't think the vet should be blamed for the cost, and I don't think you have a leg to stand on in court against a backyard breeder with no health contract. You choose (as a responsible pet owner) to treat, and that comes with a cost.