The free plan is good for single quality assurance engineers and small companies, and provides access to the following:
Up to 3 regular users in a team
Unlimited read-only users
2 concurrent test runs
500Mb for attachments
There is a maximum number of 3 Regular users on the free plan, and an unlimited number of Read-only users on any of the free or paid plans.
To upgrade your Workspace to a paid plan, you need to have access to a "Billing" role in your workspace.
The Startup & Business plans have a tiered pricing model, which depends on the number of active users in your team.