As every Council is different, and indeed every Clerk too, you'll not find any guidance. We asked the Clerk to keep a timesheet of every single piece of work she did for us. From that we were able to ascertain what was involved in clerking a meeting, what happens in between and one-off items such as audit. Quoting a monthly figure, rather than a weekly figure helps to overcome the natural ebb and flow of the role.
For a small Council meeting every other month, we ended up at 18 hours per month, with additional hours as required for audit. I've just advertised a larger Parish Council, with a cemetery, at 50 hours per month.