Currently, Tango Pro pricing is per user. Upgrading one account to Tango Pro requires all members in a Workspace to have a Tango Pro license.
Workspaces with 1-2 users will be on the Pro Personal plan, which starts at $22 per user per month when billed annually. Workspaces with 3 or more users will automatically be on the Pro Team plan, which starts at $15 per user per month when billed annually.
For more information on upgrading multiple team members, check out this article.