Check the policies on your credit cards. I know it sounds weird but many of them actually have free rental car insurance included in your benefits as a card member. There are some limits to this however they typically involve the higher end cars and trucks.
I have a capital one card with these benefits and did not even know until one of the Locums docs I was working with pointed it out. Unfortunately this was AFTER I just paid out of pocket for a tire I busted on a curb. *insert eye roll here*
Anyways, you may actually have the coverage that you need. Hope this helps!