Lots of proprietary software is available at no cost. Take Internet Explorer for example.

What should make free (as in freedom) software appealing to Christian audiences is exactly what you suggest towards the end of your post – freedom. No matter how much proprietary software costs, it will never respect a person’s freedom the way that free software does. The psychosocial harm of non-free software (sharing with your neighbour is against the law) contrasted with the social good which is the focus of free software (sharing with your neighbour is encourage) is what’s at the core of the appeal to a Church audience, I think.

Though, I certainly need to give this more thought. I’m interested to see how you further the relationship.

ps I think the term ‘free software’ makes a lot more sense than ‘open source’ in this light… open source is just the method of software development, and there’s no reason a religious organization should really be biased towards one method of development over another. Free software, on the other hand, focuses on the freedoms that are respected, which I think is more relevant from a religious perspective.