Both GitHub and Cloudflare have generous free tiers that comfortably cover an ordinary wiki — you won’t be asked for a card to get started. A very large or very busy wiki may eventually want a paid plan, but most never need one. And because your pages are plain files in your own GitHub account, your content is always yours to export or move.
This note appears on more than one page — it’s a single page included in each, so editing it here updates it everywhere.