Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Dear User_1087,
Good day! Thank you for posting to Microsoft Community. We are happy to assist you.
Typically, Microsoft will charge per the number of licenses you assigned to your account. Therefore, if you have not assigned a license to the additional account, then there should be no charges associated with it. You can create a number of unlicensed user accounts, but to access Microsoft services you must assign license and pay for those licenses. So, if you add 30 more accounts without licenses, there should be no charges associated with them as well. Please let me know if you have any further questions or concerns.
In addition, you can also create shared mailbox without license to collaborate with coworkers, you can refer to About shared mailboxes - Microsoft 365 admin | Microsoft Learn
Thank you for your precious time. Have a nice day.
Sincerely,
Libeamlak | Microsoft Community Moderator