Hi @gtimarkv_zoom thanks for posting & using Zoom! There is no cost to use the Zoom API or to publish on the Marketplace. Any licensed user will be able to call the API to control their account, create meetings, etc. If you integrate Zoom into your product, Zoom users will be able to authorize their account (through OAuth) to make API calls.
We do have an API Partner plan, but this is typically for products which resell Zoom video services as part of their business, rather than allow users to connect their accounts.
Let us know if you have any additional questions!