Sometimes, you may want to create a custom plan or rate for a member or a group where 1 of the members is paying for the entire group (i.e., team of 4). If this custom plan will be applicable only to that group, you can create a Plan and hide it - see here on How to Hide a Plan.
You can create a custom plan in exactly the same way as a regular plan. The only difference will be that you'll hide this custom plan from Public view - and/or - ensure the plan can only be assigned by an Administrator. The screenshot below highlights these options: