While I encourage supporting the Obsidian team by paying, there are ways that you can get the same features without paying.
Sync - On iOS, you can use iCloud to sync your files between your Mac and iPhone. I imagine that there are more configuration options for this on Android.
Publish - lots of different ways to deploy your notes to a site. There's one repo that helps you publish with Mkdocs [1], and I'm sure there are other tools the community has created to solve this problem.
It may not be as simple to set up as Notion, but that's the price you pay for wanting a solution to be cheap, private, and let you own your own data.
Realistically if you care about privacy and owning your stuff you'd go with one of the many open-source options. Especially if you have to bring your own syncing anyway.
Sync - On iOS, you can use iCloud to sync your files between your Mac and iPhone. I imagine that there are more configuration options for this on Android.
Publish - lots of different ways to deploy your notes to a site. There's one repo that helps you publish with Mkdocs [1], and I'm sure there are other tools the community has created to solve this problem.
It may not be as simple to set up as Notion, but that's the price you pay for wanting a solution to be cheap, private, and let you own your own data.
[1] https://github.com/jobindjohn/obsidian-publish-mkdocs