Some details about what tools you used to find the culprit, or how you optimised it, might be more interesting.
Without reading the article, I figured there was only one likely explanation—the function gets called a lot.
But you can optimize their usage in your code.
They probably could save that amount of money by maybe trying different machines/providers.
I wonder what's the annual worldwide cost of parsing XML for example.
Unless it's for something very specific, of course.