If you think smoke testing is cheap, try doing it across concurrent releases and multiple envs, then see how fast the "just check it manually" step gets dropped when nobody owns it. Manual QA finds weird edge cases, but if that's all you have, regression will eat you alive.

Smoke tests and unit tests do different jobs, and calling unit tests low value is backwards unless your code almost never changes. If you skip automated tests because they are "expensive", you are betting release quality on hope and a lot of repeat work.