My take
Wix/Squarespace - gives you ready to build options - the site is setup in the shortest time possible. But when you want any feature which is not available handy - you endup with expensive choices to make
Best suited for - basic , no frill sites
Prismic etc
Fast, best for performance. But You might need a techy person on standby - incase you need to setup any thing additional.
Best suited for - IT company or companies who already have technical people on the payroll to take of this
WordPress
•
Maintenance - WP has come up with a auto-update feature, which upgrades the core/plugin/theme when there is a update available.
•
Security - Since WP is open-source and a very active developer community, it is most secure CMS (the WP sites that get hacked are mostly running outdated software)
•
Plugins for each need - with such an active dev
community any feature you can think off is available to plug-and-play; this is good for non-coders to setup features like donation/product pages
My suggestion for WP would be to
• use a active
free theme so that any issues are fixes as they are detected
• Get a good dev to handhold a member of this non-profit and explain how to maintain the site what needs to be checked (ensure daily backup is getting mailed, know how to communicate with the hosting staff if the site is down). this way you will have no monthly expense; and incase the site goes down you can use a small portion of the 10,000 yearly budget for bringing up the site using the daily backups.
• get a good WP dev to setup the site. Setup db backups, media backups and secure the site against brute attacks.
I help a few NGO maintain their site, the above is my experience. Hope it helps you out.
If you want to go for cheaper option - My suggestion is
WordPress.org (Free) (and not
WordPress.com - paid) - this could be setup with hosting provider - Hostgator/Bluehost
Example free themes
https://wpastra.com/ (download from
https://wordpress.org/themes/astra/)
https://demo.athemes.com/themes/?theme=Sydney (download from
https://wordpress.org/themes/sydney/)