At 20, I doubt if you will find any "cheap" car insurance. Please call an insurance broker, and ask them, or go see them, and ask what is the cheapest. Sometimes, it's cheaper not to go through a salesperson (broker), but call direct such as Geico, Progressive, etc, and skip the "middle man". Good luck.
This is something that you would have to check with the local insurance companies and compare the rates. The cost of car insurance is usually high for a teenager, but factors like the car type and driver's record also come into play.