If the teenager is purchasing their own insurance then the cost of the teenagers car insurance will be high and range from $200.00 to $400.00 per month depending on the year of vehicle and make and make and model of vehicle.
Also the value of the vehicle will factor into the monthly or yearly cost of a teenagers car insurance but it will be expensive for a teen to get car insurance no doubt.
If possible try to get on parents car insurance as you can usually get a discount and take safe driving courses to help lower the cost of the teenagers car insurance.
You can check out auto insurance websites and get free quotes for the teenagers auto insurance.