Pixie Power, when you Englanders say "hire" do you mean take a Limo? Or do you mean rent a car and drive it yourselves??
My suggestion would be to rent a car and drive it. It is about a 2-hour or so trip to Clearwater from WDW. It would be extremely expensive to (as we in America say it) "Hire" a car and have someone else drive you!
Renting a car and driving yourselves would be about $30 a day depending on how many people are going. You'll have to check, but a cab, towncar, or a limo would be in the $100's.
Driving to Clearwater is easy. You take I4 from WDW and pick up the Courtney Campbell Causeway in Tampa. It brings you right into Clearwater. We did it in November. What a blast!!!!
Holly