I suspect it should be emphasized that you really shouldn’t put much time or effort into your message.
It’s been almost 20 years since I worked for someone in government, so I could be wrong, but even then we simply added to the count of people who wrote in in favor (and recorded it with their name in our database) and didn’t read the note.
Every.org tentatively appears to not have a minimum donation amount.
A number of organizations affiliated with our cause areas are on that platform, I believe.