Welcome @Paulo_Carvalho to the Airtable community!
Every use that will need to edit records directly in the Airtable interface in a Pro workspace will need to be a paid user. Users that only enter data via forms, and only view data via shared views do not have to be paid.
If many people need limited edit access to data, you can also look into creating a portal with Stacker or MiniExtensions. Although these third party tools have a monthly fee, they are much more affordable than having multiple Airtable collaborators.