It depends on how old the animal is... Spending $600 on an animal that is only a few years old and has a long life ahead of them is one thing, but spending $600 on a cat that is 18 is something entirely different. There comes a point in an animals life where the owner has to be willing to let them go.
Really you need to think about the quality of life for your pet. If $600 could fix a cat or a dog that was young, and there would be no complications later on, I would spend it in a minute.
It also depends on if I had the money to spend.... Paying bills, rent, and buying food is more important for me (and a hypothetical family) is more important, and if I had to make the choice, I would go with keeping myself fed with a roof over my head.
R