If you are looking to rent a car for an outage, it is often worth the price of a cab ride to rent off-airport. You have to shop around, but off-airport locations don't have the enormous fees added to the rental fee that airport locations charge.
Phoenix is a great example. The airport rental car facility, and the buses that run to it, are all funded by add-on fees.
Wherever you rent, make sure that you take into account taxes and fees. They can cost as much, if not more, than the rental.
Don't forget to ask for discounts. Just about every membership organization (AAA, American Legion, etc.) has a discount code. It won't be huge, but a few dollars a day can add up over the course of a year. Definitely sign up for the frequent renter program. Renting for 8 - 10 weeks a year will get you a free week. That lowers the overall cost considerably.