This site will give you the prices of recent purchases of propane by county. As you can see they are all over the place so shop around. As far as whether to use propane or electric for your water heater, that will depend on what is installed in your home. 99% of Florida homes have electric water heaters. Even if it were less expensive to use gas, it may not make sense to pay for replacing the water heater if yours has an electric one. If you use electric, put a 220V timer on it so that is only on a few hours a day when you need it.