Consultation fees added to apoointments

[Jonas Fried]

Is it possible to add a fee charged for each visitation entered in the
calender and then at the end of each month calculate the amount owing for a
specific customer based on the entries (appointments/session she/he has had)
in the calender?
If this is possible and needs a macro I would be grateful if someone could
point me to a template or tutorial.
Thanks for any input
Jonas