This question can refer to two different things in Zoho Sites, which is worth clarifying before looking at any specific number.
The Member Portal is a login system for your website that restricts specific pages or files to registered members only, rather than making that content publicly visible. Members can be added either by allowing self-registration or by direct invitation, and can be grouped so permissions can be assigned to a whole group at once rather than member by member.
Separately, Contributors are people invited to help you design and build the site itself, whether they're inside or outside your organisation. Contributors can be assigned roles such as Admin, Author, Developer, or Guest, controlling what they're able to do within the site editor.
Separately from Member Portal accounts specifically, Zoho Sites also lets you hide pages from everyone, or from specific members of your own organisation, giving another layer of control over who sees what on your site.