There is no set price for car insurance for an 18 year old. The amount will be determined by the car insurance company, and the person's driving record.
As long as she owns the car, has a license, and can afford the insurance she can buy it.
In California you have to be at least 25 years old to rent a car. Insurance companies will not give an 18 year old rental car insurance. If you do find a rental car company that will allow you to rent a car from them, the insurance you have on your own vehicle will cover the rental car as well.
It depends what car you get could get say a ford fiesta that i think is round about 2 grand for a 17-18 year old.
YES
Yes, any legal driver can and must have car insurance.
in the UK Around £4000
No, you don't have to put your son on your insurance, but he will have to get insurance of his own.
Older safer cars are the cheapest.
Yes, you can. List him as a driver.
Depending on the car you are planning to run, in any event, very expensive.
You cannot get car insurance if you do not have a license because you cannot legally drive.