How to approach the topic of "consideration"?

If someone, due to your high visibility & extensive network, asks you to help them, in a volunteer capacity, get elected to a local political post, which will involve significant campaigning and time on your part, how do you broach the topic of "consideration"? In other words, in exchange for the tremendous resources of your network, time & influence, if you are absolutely unwilling to do it unless there is a significant benefit involved, how does it work?