Make sure to check rates at nearby airports, if that could be an option.
I book a car for 4 weeks in February each year. I usually pick it up and drop it off at the Ft. Lauderdale Airport. Back in April, 2008, I made a reservation for the 2009 dates I need. I've learned from past experience to book very early.
I do not book the airline tickets until around this time of the year. We usually take JetBlue and they do not release the February fares until around September. Recently when I checked the airfares, I saw better prices flying into West Palm Beach but returning from Ft. Lauderdale. My first thought was that picking up the car at Palm Beach and returning it to FLL would be higher. Wrong. When I priced it out, it was $70. a week less for the same car I had booked back in April. But the price of my original itinerary (in and out of FLL) remained the same. I was checking from a different computer at a friend's home, and did not enter any identifying info, so there was no way that they knew I already had the higher-priced reservation.
When I looked carefully at the price breakout, the base fare was
identical but the taxes and surcharges were much higher at the Ft. Lauderdale Airport.
Also, in past years, hubby and I would often times book the car for pick-up at the Ft. L. Airport but with a drop-off at an off-airport location on Sunrise Blvd.. There was a dramatic difference in pricing (
much lower). We would not want to go through the hassle of getting to the Sunrise location on the arrival date due to possible airline delays, schlepping luggage, etc... But on the day we were going home, we'd drive to the airport together, do curbside check-in, and then one of us would remain at the airport while the other would drive the car back to Sunrise (less than a 10 minute ride) and then take the public bus or a cab back. We can't do that these days because we now take our 92 year old mother with us.
But for those of you who travel light ( and motherless

)and don't mind a little inconvenience, try checking out the price of renting the car from near-by off-airport locations such as some high end hotels, or timeshare resorts, or neighborhood locations of the major car rental companies. Most of the car rental web sites will have a drop-down menu showing these locations if you enter the city name but leave the airport code box blank.