When upgrading a team to business class, can I addd members outside the team that won't be billed?

[Nathalie Tremblay]

I'm interested in upgrading to the business options. However I several boards of folks outside our business team. How can I manage to pay for those only in my team vs all board members?

[Matthew N]

When you upgrade a team to Business Class, any member of the team will be billable.  

Check out this help article

Can I add someone to a board without paying to add them to the team?

Yes, as long as your team settings allow adding non-team members to boards. This can be useful for adding external members to your team, such as clients or contractors. Because Business Class upgrades are per-team, you will not be charged for members that you add to particular boards instead of the team as a whole.

As a tradeoff, those team members will not receive some of the perks of Business Class. They'll still be able to see and use Power-Ups that you have enabled, but they will not be able to enable unlimited Power-Ups on boards themselves without Business Class. They also will not have the benefits of Trello Gold (large attachments, saved search, custom stickers/backgrounds/emoji), and will not be controllable with BC permissions (being able to deactivate a user/remove them from all team boards at once, view their recent activity, restricting team boards to team-members only or a certain domain only)