I haven't started selling soap yet, but when i called my local zoning office (in pinellas county) they told me I need to go to the tax office and request one, and if I plan on naming what I sell, then I also need to file a ficticious name with them. I don't remember what the cost was, but the reason I forgot is because it wasn't much and I wasn't worried about it. Sorry i can't help more, but hope it does a little.
ETA: I just realized I need to clarify part of that. When I called my local zoning office, they told me to go to the tax office and request one. I asked if I was allowed to make soap from my home and sell it to the public. They took my address, and called me back saying that as long as no customers ever step foot on my property and I am not actually selling anything in my home, then I am free and clear to do what i want. When I called the tax office, they are the ones who told me the price (which was low and I can't recall) and that if I named my soap, then I need to also file a fictious name with them.
Having a day to recall the phone calls helped me remember the details better.