alt Hacker NewsAWS sends out targeted notifications via email and via alerts in the console if you are a current customer of a service that is changing somehow. It’s pretty normal that they don’t send out a press release and blog post every time something changes - if they did it would be a mass overload of such releases.
And if you are spending enough, a rep will probably personally reach out to you. I've never personally been blindsided by price changes, they seem actually one of the better vendors about this.