Comprehensive does not normally provide protection for mechanical breakdown. One noted exception is collision with an animal, which is usually covered under comprehensive. This will increase your entire policy cost regardless of your driving record. Some more exotic vehicles may represent unacceptable risks to insurance companies and will be much harder to insure, other companies may not be willing to insure them at all. This protection is necessary to protect yourself should you injure people or damage property.
Liability laws differ in each state.
Then, discuss the specific amount of liability insurance needed with your insurance agent or broker. The dollar amount you have to pay, out of your own pocket, when you file an insurance claim. A higher deductible can be used to lower the comprehensive and collision portion of your insurance bill. The higher the deductible, the lower your premium. Deductibles are normally on a per-occurrence basis.