People will rather do something for free than cheap. - Peter Bregman

A Story About Motivation.
http://blogs.hbr.org/bregman/2010/02/a-story-about-motivation.html
People tend to think of themselves as stories. When you interact with someone, you're playing a role in her story. And whatever you do, or whatever she does, or whatever you want her to do, needs to fit into that story in some satisfying way.
When you want something from someone, ask yourself what story that person is trying to tell about himself, and then make sure that your role and actions are enhancing that story in the right way.
We can stoke another person's internal motivation not with more money, but by understanding, and supporting, his story.