I mean it takes maybe a day or two at most to set up a CI/CD pipeline with Github actions or something similar. It takes maybe a day to set up test runners, and you can just sprinkle in small tests as you go. There are plenty of templates you can find depending on your language/platform that do most of this out of the box.

You don't need a perfect pipeline or test coverage, just something you can improve on incrementally. It's much, much harder to do all this on top of a bloated legacy codebase and infrastructure and that's when "adding CI/CD" becomes a Big Project that we'll get to real soon now.