How can I start a rental car agency?

I’ve been looking a for a detailed plan how to start a rental car agency. The toughest thing I’ve seen on starting one is getting an insurance carrier to cover the cars. Now I’ve seen around here there are two rental car companies that rent vehicles, to body shop customers and use the customers insurance for the time the rental is in use, rather then their own. Is it possible for me to rent out vehicles without having to buy an expensive insurance policy?