My brother-in-law has found himself landed with the task of recreating an association and it's web site. I've abandoned making full-blown web sites but he just needed a temporary site to get going.
Anyway, I looked up a flat-file CMS called Get-Simple that I'd used in the past. Unfortunately it hasn't been updated much, and doesn't work with php 8+. But DuckDucking around I found that someone had made some unoffcial patches, and lo and behold they work fine.
I modified an events plugin to get it to work with php 8+, so it could be used for bookings. You can download it here.