In reply to Tomas.

Thank you for the pointers, I'll check them out!

The ones I highlighted seemed to be the closest to WP in terms of user experience for site managers and editors.

On pricing: The first listed price at Sanity is $199/mo... similar to others I was trying to count listed prices vs free trials or variable usage plans, because it's very hard to know what that would cost. At Sanity for example they limit based on API CDN requests, API requests (not sure the difference), bandwidth, listeners (?), datasets (?), documents, users, and storage. You don't see mainstream hosts or WP.com limiting in the same way, perhaps except storage.

WordPress itself is an open source, and free CMS that can be used in a headless way. :) In general I am supportive of any open source CMS, including "competitors" like Drupal or Joomla, but more skeptical of proprietary solutions, especially if they lock you in.