List all fixed cost items, including (for example):
meeting room rental
A/V equipment rental
supplies for displaying posters
set-up charges for cash bars
honorarium for banquet speaker
Add all the above. This is cost element 1.
List all per-person costs, including:
mailings
supplies
food service (coffee, snacks, etc.)
name tags
Add all the above. This is cost element 2.
Estimate probable attendance using advance indications of interest, early registrations, and records of attendance at previous meetings in similar venues. This is cost element 3.
Multiply element 2 by element 3 (per person costs times number of attendees expected.)
Add above product to cost element 1 (fixed costs). This is the total anticipated cost of the meeting.
Subtract from element 3 (estimated attendance) the number of people who will not be paying registration and/or banquet fees (e.g., Student Paper awardees, Brouwer awardee, special guests). This is number of paying participants.
Divide total cost by number of paying participants to get average meeting cost per person.
Increase average cost per person by appropriate safety margin (say 10%) and round off to nearest $5. This is the registration fee.