This post is going to be short, but this process will consistently save you lots of money on car rentals. I've used it so many times to save me hundreds of dollars, so felt the need to share it. I used this tip yesterday to save me $50 bucks. Warning, this only works if you have a Costco Membership.
Step 1. Go to Costco Travel and book a rental car that works for you. This work best if you do it as far in advance as you can.
Step 2. Every couple of weeks check to see if the prices on Costco Travel have changed. For those of you that are not aware, rental car prices can fluctuate a lot.
Step 3. If you find a lower price, book the new car rental. You now have two reservations.
Step 4. Cancel the original one. This is where Costco comes in, there is no money down to book a rental and no penalty for cancelling at any time.
Step 5. Repeat steps 2 through 4 until your trip.