I am in the process of putting together a trip to the Big Island for next year. I have a car reserved with Budget at an okay, for Hawaii, price. Looking at airfare I found a great price on a return flight a day earlier than originally planned. If I reserve a car through Costco reflecting the revised schedule, the quoted cost is about $900 more than my existing reservation. What happens if I keep the existing reservation and return the car 1 day early? Will I be charged the original price or will it be pro-rated to reflect a shorter rental period?
I realize the reservation is 11 months out and car rental prices can and do move up and down frequently. With the increased demand for cars in Hawaii I am not anticipating any major price drops.

You can keep your existing reservation. If you return early, it will most likely be prorated and you'll get back one day of credit, but it's hard to be more specific without knowing the actual dates. Regardless, the worst that will happen is that you'll return a day early and pay your original rate.

All of that said, next year is a loooong way away in car rental terms and lots can change between now and then. Here's what we highly recommend:

1. Track your existing reservation with AutoSlash.

2. Once you receive the tracking confirmation email from us, reply to it and say, "As per AutoSlah's advice on Flyertalk, I'm letting you know that I plan to return the car one day early, so please revise my return date on the tracking request from MM/DD to MM/DD. This way, we're searching for better deals on your actual planned return date as opposed to the one on your existing reservation.

Hope this helps. We look forward to saving you money on your rental!