If your goal is to control where analytics data lives, compare self-hosted editions rather than the cloud subscriptions with the same product names. Umami, Plausible Community Edition and Matomo On-Premise each offer a path to running analytics on infrastructure you operate.
Start from the reports you actually use: acquisition, campaigns, conversions and events. Replacing a GA4 tag alone will not recreate your existing event definitions or attribution history. Write down the required reports, install a candidate on a test property, and compare metric definitions before migrating.
Free software does not remove server, database, backup or maintenance costs. The comparison below uses official documentation, not a shared load test. Self-hosting also does not automatically settle consent or privacy requirements; your configuration and data collection still matter.