What's the difference between users and collaborators?

[Retail Support]

I want to purchase the premium package as a user and then add collaborators which are unlimited with this package.

The collaborators are existing users of the free service, but when added to my boards it increases the price substantially.  

If I'm unable to ad these people to my boards without increasing the cost, I will continue to use the free version.

[Andrea Crawford]

Hi @Retail Support This article may help explain who you can add without increasing the cost. https://support.atlassian.com/trello/docs/multi-board-guests/

If you add a collaborator to more than one board within the workspace, they become billable as a multi-board guest. If you add a collaborator to a single board only within the workspace, then you won't be billed for them. Hope this helps!

[Pallavi Shirodkar]

Hi @Retail Support 

On Trello Premium you can invite unlimited collaborators, but only certain collaborators are billable; the rest are free.