Cavities cost how much?

Today I went to the dentist and I had three cavities. I was totally bummed. We have very stinky dental insurance. It pays for cleanings but not the extra work. I knew it would cost something but they quoted me 520 dollars! Oh my gosh, who knew cavities cost so much! I called the insurance to see what they would cover and it was 30 dollars. Wow, that is not very helpful. So for now I still have three cavities. I don't know when I will get them taken care of, but I am obsessively brushing, flossing, and Listerining. I don't think that cures cavities but until we can afford to fix them it will have to do.