Just a suggestion and something to consider.
First of all, we need to get the list of members that will be participating done. Then we can gauge on the sort of crowd or turn out that we're gonna have and decide on the location. An estimation on the number of turn out will do.
Well, we will need to do a cost comparison on the options that we have on locations picked, doorgifts (if any), refreshments, photographers etc. We then divide the costs evenly based on the number of turn out and deduct sponsorships if we manage to get any. Finally we can come out with the fee to be charged to participating members.