Thank y'all for all your feedback! Keep it coming 
We're working on a new way to build and share public apps, which should hopefully help with the price per user issue. Coming soon™️!
Anyone with a Retool account counts as a user pricing-wise, editor or otherwise. On the Business Plan, you do get the public apps feature, which lets you build apps that are publicly available to anyone with the URL. Whoever uses that link won't need a Retool account, so you won't be charged for them. Since the app is public though, you wouldn't want it to have any user-specific information or dangerous functionality (I.E. deleting rows in a database).
Currently, public apps are meant for simple apps with no authentication or security. In portal-like use case where there's a notion of authentication, public apps won't be your best option since they don't collect any sort of user info. feel free to shoot Antony, the PM working on externally facing Retool apps (like client-facing portals), a note at antony@retool.com if you'd like to share more about your use cases.