The costs of continuous integration

Having a short, fast smoketest set of tests, and an extensive set of tests is as easy as marking the tests for different test suites. It's pretty much standard practice in my book.

Gitlab and others have the ability to run different test suites for the PRs and on a configurable "cron" schedule, so you run the smoketests on every PR, and "full" test suite on a daily basis on the master branch. If the full test suite broke, you can bisect to the commit or PR that broke it easily.

If data transfer of VM/Docker images and other assets are dominating the bill, a local image repo or just a cache should wipe 99% of that cost.

All tractable issues, IMO. And CI is a net win.