There's no charge for requesting Congressional support. On the other end, what better way to get your vote than trying to help you out?
Working in a job that deals with Congressional inquiries (100% unrelated to NAMI but related to other Navy items), they usually consist of the following:
"Sending on behalf of my constituent _________, can you please inquire about ________."
The responsible office usually has 10 days to review and provide a response back, normally in the form of a written/signed letter.
I would say... if the member does have ties to the Rep/Senator (donations, family connections, etc.), the Congressional letters might be a bit more "aggressive" and/or the Rep/Senator might be more involved.
But with that said, I 100% discourage donating or doing any sort of effort trying to *support* a Rep/Senator hoping to get more support.