Try Autoslash.com, it’s an aggregator not a rental site itself. You can have them give you a quote each day, if you book (you do not have to give a credit card), you can still request they continue to check for lower rates. If they find something, they will email you. I I did a combination of both and went from $428 for 9 days down to $300, all inclusive, airport pickup. It beat the lowest rate I could find on my own by $250.