Obsidian has a community plugin called "Remotely Save" that lets you sync your vault via Webdav, S3 (compatible), Dropbox, or OneDrive. It works on all my devices and synchronises my data just fine. You could also use something like Syncthing or any other third party solution that syncs your Yaml directories.

Obsidian runs on local Markdown files so there are many free options you can use for syncing and publishing notes.

I’ve been using icloud to store my vault and have found it to be great to sync with laptop, phone, and tablet (obviously they’re Apple devices as iCloud isn’t supported on anything else).

It’s been really solid. When I used an android phone I had a lot more difficulty. While syncthing is reliable on android and macbook, iphone and ipad don’t work nearly as well.

Obsidian publishing costs USD 8 per month. A Starbucks latte in SF costs USD 5.88.

I don’t use Obsidian Publish, and I don’t need it. I use the Obsidian app for free, and I don’t need the Sync feature as it works fine with iCloud.

If at some point I need the publish feature, I consider the price that is less than two lattes per month a good deal given the zero cost of the app that I used for a long time.

It isn't your only option:

https://github.com/oleeskild/obsidian-digital-garden

https://github.com/jackyzha0/quartz

https://github.com/jonstodle/obsius-obsidian-plugin

https://github.com/yoursamlan/pubsidian

https://github.com/ppeetteerrs/obsidian-zola