A lot of the price fluctuation probably has to do with state/county taxes. I've been told that some of it is due to delivery costs (is that why it is cheaper in TX and OK?).
The FL Attorney General web site states "Federal excise taxes are 18.4 cents per gallon. The State of Florida also levies 14.1 cents per gallon in Motor Fuel Taxes. Local governments levy anywhere from 9.6 cents per gallon in Franklin and Okaloosa Counties to 17.5 cents in several counties, creating a range of 42.1 cents in total fuel taxes and inspection fees to 52.29 cents." My county is one of those with a tax of 17.5.