I think it has consequences on the design of the language, making it more complex and more prone to "clever" code, i.e code harder to understand when you haven't written it yourself (or you wrote it a rather long time ago). I've experienced it myself, I spent much more time in my life trying to understand complex code (complex in the way it is written) than to correct trivial NPEs.
That being aside, it is less easy to find developers proficient in a more complex language, and it is more expensive to hire a good developer and let him time to teach himself that language.
I'm not sure it costs "very much", though. I might be wrong. But that's the point: nobody knows for sure. I just think we all lack evidence about those points, although PL theory says avoiding NULL is better, there have been no studies to actually prove it in the "real-world" context. Start-ups using Haskell/OCaml/F#/Rust and the like don't seem to have an undisputable competitive advantage over the ones using "nullable" languages, for instance, or else the latter would simply not exist.
