Title explains it. An utterly self-serving suggestion, but it seems odd to me that the very people who operate the system have to pay for using it.
Might want to make it free for Watchers too, seeing as many types of announcements are part of their job description.
Given that the Civil Service have few responsibilities yet get a pretty decent wage already, It'd be a bit inappropriate. Prefects, Directors, and Watcher officers I could see getting free sendings though because they've earned a certain amount of prestige and are unlikely to abuse the sending system (spamming speeches, passive aggressive insults, irrelevant stuff, etc.).
This strikes me as an excellent IC pursuit.