The hosting for traffic, server, are marginal. Not the issue here at all.
The real cost of hosting any webapps is initial installation, long term maintenance and also user support.
For example for phabricator.whonix.org there’s now the issue how to get rid of it since deprecated upstream.
You’d think if major orgs such as facebook and wikipedia are using phabricator it should have a bright future, not going away but apparently not so.
Maintaining self-hosted installations of mediawiki, discourse forums, phabricator, (previously mailman and update hell wordpress), whonix.org mailer has cost tons of maintenance hours. There’s webapp upgrades, upgrade issues, broken databases, backup and restoration. Most webapps don’t support multiple domain names such as whonix.org and Whonix onion. Most webapps expect 1. Not two domain names with the same content. TLS clearnet vs non-TLS onion. Sometimes this can be done with complex web server configs.
So I am wary of self-hosting new webapps.