Car Rental - Cheaper to Book Early or Wait?

I'm going to Bal Harbour in late February. I'd like to get a car rental from Fort Lauderdale airport, but its about $75 per day right now. Will the prices drop if I wait until the week before I leave to rent the car? (I'm not really that bothered if I don't end up getting the car, but it would be nice to have one.) I checked the rates for next weekend, and they were as low as $35.