That's up to you. One way may be to first choose an amount that you're going to spend on advertising (for a full-page ad in a home-business magazine, for example). Let's say that you want to do a $1,000 ad and you anticipate that you will be able to get 50 participants. You would, hence, charge $20 for a share in this co-op, with a limit of 50 shares available.

Another, probably safer and easier method is to simply choose a "unit cost." Let's say you chose $25. You would tell your affiliates that they can participate for $25 in your co-op ($25 for each equal share of referrals that the co-op generates). Then simply take all the money collected and buy as much advertising as the total amount collected allows. The Co-op Manager will take it from there, equally dispersing all affiliates/members that your advertising generates.