Maybe you could look at it as an investor model. Charge a nominal fee to keep your frustration/annoyance down as you log all the development hours, but once you have an app that works either give it to your "investors" for free or pledge free app upgrades as you improve upon it.
In working with museums I think you are afforded more flexibility than straight consumer markets. Most museums are in a pinch right now, but would love to wow their members with some technology. Depending on small your fee would be, you could get the ball rolling pretty quickly. Adam Mikos
