I always ask if they want monthly,some say "depends on the price"
I then reply the price depends on the frequency.
Usually the good uns ask how much for every month,the proper one offs will still ask how much for 1 time,then you know to charge accordingly.
That said i sometimes price a daft amount if i dont want to do it for access or other reasons that annoy me,overgrown garden/gear all over the place etc,even if they want regular cleans.