In general, these are the added fees:
Concession Fee Recovery Charge - 9.8% of rental
Florida Surcharge for Tire & Battery Recyling Fee - $2.05 per day of rental
Florida License Fee - .41 per day of rental
Florida State Tax - 6.0% on entire bill
To break it down to actual dollars & cents, it will add about $77 to a $275 rental price.
They may vary slightly depending on whether you use a company at the airport or off but you'll have a pretty good idea what to expect.