I don't know what the law says (if anything), but I've certainly seen £15 and more quoted for such things.
One outfit that was bugging me asked for £75 when I asked them to tell me where they got my details. (I complained to the Data Protection Registrar, or whatever it's called these days, but absolutely nothing happened as a result)
This is the CAA anyway, and they're sort-of Government so are above the law (aren't they?)