Those vet bill amounts aren't sustainable unless you're a millionaire. I raise one of the rarest breeds in the world and losing a single bird is a problem. Every time I lose a bird for unknown reason, I send it to our vet university for a $100 necropsy so I can nip any potential problem in the bud.
However, I have incubators and eggs to replace birds. I did spend a little over 100 on a vet visit and x-ray for one bird. But that is my limit. Maybe it is because my birds are livestock and not pets. I butcher and eat extra roosters. There is no way in H E double hockey sticks that I would spend that kind of money to save a chicken. I don't have that kind of money but even if I did, that would be insane.
I have a friend who is an animal behavior consultant and has worked in the rescue world. That was mostly for exotic birds, waterfowl, poultry, dogs and cats. One year her vet bills were over $34,000. She still has a couple parrots and other exotics as well as a dog and other animals she continues to take to the vet. That being said, she is flat broke, 2 months behind on her rent and utilities and doesn't have money to repair her car or feed herself.
I believe that is the definition of insanity.
If caring for animals isn't sustainable, it doesn't work. You can't care for animals if you don't have a home for yourself.