Where have you been all these years? One incredibly simple answer to your question:
Goto autoslash.com. They've a long, trusted track record. Not only will you get the best rates given your own affiliate memberships (AAA, Costco, AMEX, etc, etc etc) you can't get anywhere else 97.416% of the time, they'll even track your booked rental and notify you if there's a price drop.
And sleep well.