Most networks require a very small deposit to Join them and show your commitment. These are 100% refundable if a great deal can't be struck. But having a token gesture gives confidence to others that:
1. This could be a great thing to save on.
2. That everyone is committed so the network deal can't fall over
3. That the network can grow confidently with just a small deposit.
Note: Any Network Joining fees are 100% Refundable if a network deal is unsuccessful for almost any reason. The main ones include, "not attracting enough members" to be in a strong negotiation position. Or that "suitable quality Suppliers are not able to offer a worth discount at this time."