What percent of project budget do you typically allocate to writing those business scenarios?
Hey, no problem. I'm surprised to find someone interested in this topic. 😄
They're written as business scenarios and you can combine them into E2E tests. You can reuse one scenario like "login with valid customer profile" into lots of different E2E tests.
At my old company, we were using Behat. That was a couple years ago. It's based upon Gherkin and the parsers often use Mink (similar to Selenium) or something. But you can also
https://docs.behat.org/en/latest/
I know some java developers that were using Cucumber Open, I think:
Discussion
About 15%, probably, as you sometimes have to rewrite and you have to make sure that they all fit together.