Every service that disabled or limited the API has seen an increase in running costs, because people turn to scraping, which costs them more resources overall, and cannot be controlled by the site owners as easily.
Let's be honest, though, hosting text files with a search bar isn't that much expensive to justify a response like this.
It's fine if they want to earn money, but then they should be upfront about it, and not making up stories about fluke running costs. I'd rather see a donation button.