Airtable has both free and premium plans available. The usage limits for each are described on the pricing page at airtable.com/pricing.
You can add as many collaborators and bases as you'd like for free, as long as each base falls below the per-base record limits described on the pricing page. If any of your bases exceeds those limits, you'll need to upgrade the team to which that base belongs (if you are a solo user, you are considered a "team" of one person).
For paid teams, you will be charged the per-user, per-month fee for each person you've invited to collaborate on bases belonging to that team. You will not be charged for read-only collaborators.
If you'd like to upgrade to a paid premium account, please follow these instructions.
If you have any questions or feedback about the pricing, we're always open to hearing from you! Contact us at firstname.lastname@example.org, and we'll be sure to review and respond to your message.