One way deals from selected Florida locations to selected Northern locations are generally offered April-June. Reverse deals are offered in the fall. Rental agencies need to move cars into Florida for the winter "snowbirds".
Otherwise one way rates will be high. Rental agencies are charging you (directly or indirectly) for the high mileage you'll be putting on the car. The agency may want to get the car back to Florida. Winter months the agency needs cars in Florida, not in Ohio.
You can check sites like Kayak but I doubt you'll get anything reasonable.