How much can car insurance be?

If you are referring to premium, it depends upon many factors. Included are the insurer, the amount of coverage, the type of coverage, characteristics of the vehicle, characteristics and driving history of the insured, who else will be driving the car, how much the car will be driven, and other factors. Insurance rates, from which premiums are derived, are regulated by the insurance regulator of the state in which the policy will be issued, so that is another factor. Therefore, there is no definitive answer to your question as phrased.
If you are referring to the cost of car insurance, several factors are involved, including

1. The insurance company involved.
2. The State in which the policy is issued. Insurance is regulated by individual States, and this includes the approval of rates. A "rate" is the cost per $100 of coverage and translates into the premium.
3. The kind(s) of coverage that you seek--for example, collision coverage, liability coverage, uninsured motorist coverage.
4. The make and model of the vehicle.
5. The age and driving record of the proposed insured.
6. The anticipated mileage to be driven and whether the vehicle will be used for household or commercial purposes.
7. Any available discounts that the insurer offers, such as multi-car discounts or whether the insured mas a homeowners policy with it.