Ah cheap flights to Florida...
Usually the cheap flights involve flying to an Airline Hub in the USA and then onward.
Recently I was looking for the cheapest flights to Florida (Miami or Fort Myers) travelling out on the 28th June and the cheapest that turned up were with American Airlines from LHR to JFK onward to MIA and then to RSW (Fort Myers) - yes it was cheaper to get that than to stop the journey at Miami! ;-) Anyway this was around £511.
Then I went to the travel agents and whilst they couldn't find any flights cheaper the agent thought of a really good idea and checked on their system direct to Virgin Holidays for a fly-drive package.
The deal was £469 direct from Heathrow to Miami with a hire care thrown in. All I have to do is pay the insurance for the hire car only if I want it.
I booked those flights with them there and then.
Best wishes,
Charlie Zulu.