Think of the value you’re offering, and if there are similar clubs/organisations with any fee structure (you’d want to be near market price unless the value prop is higher than others). If the service you’re offering is unique, think of the cost incurred on your behalf, then maybe add a 10–20% surcharge on top of it. A lot of these organisations start with 0 membership fee and build a community first. You can also think about it or maybe charge a nominal percentage of any value being created by being member of your group (think of assembling a group of freelance consultants for say web design). Remember if you’re looking at a subscription fee, you have to make sure the members see some tangible benefits upfront.