One-way auto rates to Florida in the fall or leaving Florida in the spring can be EXTREMELY low.
We live in Miami and wanted to see some friends in S. Carolina and Philadelphia. The I-95 drive is quite boring and didn't want to drive RT around 1000 miles each way.
So in May, we rented a car from Hertz for about $120/week. We had our choice of virtually any size car we wanted for the same price as long as we were dropping it off further north. We could have rented it in Miami but got one-way tickets on SWA from FLL to JAX for about $59 each which cut about 6 hours of driving time and 350 miles off the trip. It would have been $40-$50 in gas if we had driven all the way from MIA or FLL so the two airline tickets for $118 ($59x2) were a good deal.
The same strategy works in the fall when car companies want to get their vehicles down to Florida.