I’m only familiar with Obsidian, but it’s business model does have an $8/mo sync tier, and a $16/mo publishing tier as well as a $50/user/year commercial plan.
You can easily set up sync using SyncThing or Dropbox or any other tool that syncs directories between devices. I did pay $25 because I enjoy using Obsidian - but I don't think there is anything missing in the free version. The best part is that everything including themes, plugins and themes are synced perfectly between desktop and mobile.
I installed iSH [0] (Alpine linux emulator) on my iPad and sync obsidian directories between my laptop and the iPad using git and ssh. Works like a charm.
