Every plan includes unlimited members. Inviting a new person to your organization never adds a line to your bill, at any tier.
This is a deliberate contrast with how most of the software VCloud runs is normally sold. Slack, Google Workspace, and GitHub all charge per active user, which means the bill grows with headcount regardless of how lightly any individual person actually uses the tool. VCloud instead prices the compute your organization uses - a person who barely touches an app costs exactly the same as one who uses it constantly, which is also what makes it economical to invite occasional users: contractors, seasonal staff, or an entire team, without doing the math on whether each one is "worth" a seat.
See Plans and Inviting your team.