The rental rate as listed by the individual car rental agencies is the base rate for the length of the rental. As you proceed through the reservation process, insurance and other options will become available, allowing you to know the total price before you make a reservation. Insurance Policies vary by agency. After you have selected a vehicle and an agency, you can check these at the Policies & Insurance Tab of the rental center.
Many agencies require proof of existing Insurance to allow any insurance waivers. You may need a policy copy to prove this. Again, do check the individual agency policies at the Policies & Insurance tab of the rental center, especially if you are a driver from outside the US or Canada.