At this time, Cricket will not sell you service as their service in Florida is roaming on partner networks, not native (Cricket owned). They only sign up customers in areas where they own and operate the network. This is supposed to change at some point as they plan to sell "nationwide", at least anywhere on the Sprint native network as a Sprint MVNO.
So, you could go to a native network area (I believe the closest would be the Savannah, GA area), buy service and use it in Florida. You would have to accept a Savannah nuraber. Otherwise, you can get MetroPCS and hope for a merger!