In my experience, the cheapest way to serve content on the web is static, for convenience rendered with a static site generator.

It's admittedly more editor-less than headless, but anything that constantly needs to runs on a server will cost more, in the end, even if it's a freemium service, right now.

Editing content with Obsidian and rendering it with Hugo is no too bad, btw. (see eg. https://www.nickgracilla.com/posts/obsidian-is-my-hugo-cms/ for a setup).