So sorry you had to go through the pain of watching a animal suffering. The dog may have been past the point of feeling pain. I can't believe a vet would charge that much! My vet asks for a $10 - 25 donation (for the stray kitten fund). If you can't get to a vet all you can do is try to make the animal as comfortable as possible. Now is the time for you to locate resourses if ever needed - contact a rescue group, your local humane society or a vet office and ask questions as I am sure someone would be helpful. Like Aly, said have a emergency fund - it might be hard to do but its part of your pet responsiblity.