A common strategy to grow a sustainable and profitable online community is to recruit a relatively large a mount of members. The business model would then to be upsell to the members with an expectation that only a small amount will take up the offers. This small percentage would be enough to make the online community sustainable and profitable.
However, there can be different models, here is one idea:
True Fans community
This type of online community is where the majority of your community members love what you are doing and have a very high and probable chance of paying for something that you create. So instead of having 1% of members generating income, 99% do.
A True Fan community means that the quantity of members are significantly smaller, but that’s ok because the majority are contributing to your cause.
It doesn’t mean a True Fans community can’t grow into a much larger community, but it does mean that much more focus should be given to each fan. This is possible in smaller groups, but gets much more difficult (or impossible) in larger online communities.
See: 1,000 True Fans for a very interesting read on the idea of True Fans.
Photo credits: http://www.flickr.com/photos/humanoide/138782217/