Never been but on some MX boards Florida track and trails gets pretty good reviews. If I remember right it's pretty expensive to ride there and no outside food or drink had some people up in arms. For off road riding in Florida look into Croom riding area.
There's also club mx and south of the border mx in Georgia. These are more like high end amateur/pro training facilities but they might have open practice days.
Im sort of interested in riding at Florida track and trails one day but I'm kind of concerned about health insurance, at this point I haven't looked a ton into it but the idea of ending up not being covered certainly scares me.