There is a plugin for Discourse called Canned Replies that could be used. It may need some modifications, as it seems the plugin is only accessible to moderator and admin users the way it is now. However, its new user interface that can be used from the editor’s preview pane (second screenshot here) is implemented already, so from that point it’s a match.
I don’t support letting anonymous users post something on Discourse, though. We would have zero spam protection, and it would break our data model that we have for analysis in Graphryder etc. Instead, ideas are welcome how to make signup to Discourse simpler and more enjoyable. Right now we’re discussing this in the context of a tool @natalia_skoczylas wants for a Biennale exhibition.
The proposal to also place it into the header instead should be relatively simple to implement. Makes sense to me.
About mentioning monetary rewards there, I’m with @noemi.
For all proposed changes, let me know when you and your team have decided what you want implemented. The developers won’t be active before that 