My dog broke her tail?

Somehow, my dog broke her tail. I noticed after we got home from going out to eat and before we left she seemed fine. She barely sits in fear of sitting on it, she doesn't wag it (which is VERY unlike her) and when I barely touched it to see if it was ok she let out a huge whimper and ran. I know this is very serious, however we don't really have money to take her to the vet. I don't want it to get any worse, can it heal on it own? Approximately how much would the vet bill be?