Amazon Polly how?

I stumbled over Amazon Polly and saw there is a component for it. But as I understand the component it use Polly every time, meaning HA must have an internet connection.
I also saw that Polly could save the speech to a audio file. This must mean that you can create the audio with Polly and then download it to your local storage and use it over and over again. This way you dont have to be online and you save some cents every time its used.

How could a setup like this look where the action for an automation is to play a named audio file?