Florida, California, and Chicago are all very different, which is something to keep in mind. Think about why you're considering each area, then double and triple check to make sure that the assumptions you're basing your "why"s on are correct.
Depending on where you apply and to which program, funding for post-grad in the US is pretty abundant. There are many PG programs that fund the entire course of study for nearly 100% of students and include a living stipend so that students do not feel the pressure to keep a job while studying. That's definitely the case at the two US schools I'm currently applying to for PG, though I don't know if it's as applicable for PG programs that offer only certificates rather than degrees.
But like I said, funding and options vary by university and by program. It's difficult to give good advice without knowing either one.
Additionally, you will most likely be required to submit GRE scores. I'm not sure about international testing fees, but I know that for domestic students the GRE costs around $150.
Just out of curiosity - if you want to teach, wouldn't it be most beneficial to acquire any teaching certificates in the (geographic) area you plan to teach? Unless you're planning on staying in the US or I'm misunderstanding what kind of certificate you're interested in, it doesn't seem like an American certificate program would be of much use to someone teaching in the UK. $.02