I think I'm missing or misunderstanding something. I'd like to create a new app using Business Retool plan and embedding it into my portal. The plan is publishing the app, inserting it in a iframe in the portal and injecting each different portal user into the app so I wouldnt need end-user licenses because I'll manage users and workflows ( api, databases, ... ) by myself and doing API calls from the loaded Retool app once is loaded.
Using an external website to reduce your Retool user count is actually against the terms of service. The use case you're describing seems to align closely with Retool Embed, however, with Embed individual users are still tracked within Retool.
If pricing is a blocker for you at the moment you can reach out to antony@retool.com. He'd be eager to get you spun up, and see if a product like Embed or Retool Portals could work for you!