Are you an Australian resident? If so you buy it at the desk. It is optional.
How much per day is the insurance as I cannot see the price on your web page?
A quick way to see it.. Go back to the website and choose ALAMO as if you were going to make a new reservation and look here:-
At STEP2 of our 3 step online booking process, to the right of the car photo of your choice, is a link entitled "IMPORTANT INFORMATION". Click on this link and it will open an additional smaller window, where the terms and conditions appertaining to that particular car at your chosen location are displayed. The click on INSURANCE