Never been there, but went to Caribbean islands in February and I believe weather is similar...
High season (so expensive) for Florida and Caribbean is from Christmas to Easter because weather is at its best; sunny, fairly warm and relatively low humidity (that is important). Most of Florida is below latitude 30 deg. north, which puts it into the sub-tropical zone.
However, I believe there is quite a large difference between the 'tip' of Florida (Miami, Everglades) and the 'panhandle' (round near Jacksonville), where it is possible for outbreaks of cold weather from the north to penetrate as far as the Gulf coast. At New Year, the further south the better