If the area is small and it is already dried out, you basically replace the ceiling sheetrock, repaint it.
Ask a couple of licensed contractors with mold treatment license (they also fix the ceilings) to give quote (they usually love to come out for free). They could often overstate the situation. Use your own judgement. But two quotes would give you a good understanding of the issues.
Mold inspector will not come out for free. I'd say get the free quote first, then if you feel that you need to get a paid inspection, you can do it.
Mold clearance certificate is only needed for really bad situation. (It is done by 3rd party agency).
