Yeah, but so is manual testing. You can save a fortune by eliminating the entire QA team!
The QA team's main value shouldn't be just repeating the testing that dev team should do in unit testing. QA's value should be to do exploratory testing. This involves trying to break things in as many ways as possible and finding things that the dev team didn't think of.
Is there a text field? Try putting Chinese characters and emoji in it to see what happens. Try to add null characters. Try adding the entire text of "War and Peace".
Can I upload files? See what happens when I try to upload a 1TB file, or millions of tiny files.
Should the dev team be writing unit tests to handle these cases? Sure, but it helps to have someone who is explicitly trying to find all the cases the dev team missed.
Software is expensive. But do tests increase the cost?
In my experience adding tests to a legacy project not designed for testing is never worth the cost, but a new project designed with testing in mind can be developed significantly quicker having tests providing valuable data about the work in progress.
Anyways… Yes, tests are expensive. However, once the first million pours in, you are more busy ensuring that more millions come in by building features over features. And a solid foundation will help you here.