I've been thinking about the general business plan problem for years. Not only because it's a very real problem, but also because as I'm walking through a swap meet or a grocery store I'm perpetually curious about margins and return on capital for the many tiny to medium businesses for which almost no intelligence exists. If I could figure out a way to bootstrap a crowd sourced resource for these I'd be working on it right now...but alas.

In your case, if you haven't done so already, I'd suggest attempting to buy advertising from a site similar to the one you'd like the build. Maybe even invest some dollars advertising your own product (non-profits are interesting guinea pigs too) to get some idea of the volume of traffic they enjoy and the prevailing rate that advertisers are willing to pay for access to their audience. Once you have data you can start building some models and establishing ranges inside which the business makes sense to pursue. I've done this kind of research myself and for clients on multiple occasions, it's not bulletproof but it's a valuable start.