how much is it to fix a cavity without insurance

Depends on what you mean by "fix", which tooth it is and the location of the cavity on the tooth. I have a small cavity on the inside of one of my front teeth - the cost is going to be $125. For a molar with more than one surface, it would be more.

Depends on the dentist. Somewhere between $80 and $200 dollars, typically. Call and ask before you go, some are more flexible on price than others.

Also, unless you've been to that dentist before, you need to get exam/x-rays first, so that's another $100 or so.

At Stony Brook University, there is a school of dentistry, where you can get good treatment at below the cost of most private dentists. I get treated at a dental school in my area.

But, definitely less than the $3000 or so for a root canal if you don't get cavities fixed!