Well, here's the thing, as far as I see it: If you're looking at smaller shortfalls, all sorts of things are possible, such as book sales, renting the space when not in use, and all sorts of things that you can get from the local PTA (which has been dealing with these issues for forever).
However, if you're looking at a huge deficit, then there is only one solution: To quote Whoopi Goldberg in Sister Act, you have to "Get the butts in the seats". This doesn't mean evangelizing exactly, but it does mean opening the church doors, going into the neighborhood, and gently letting the people in the area know what the church has to offer them. You're going to find many parents who would like to send their child or children to Sunday school for the structure of it, but are skeptical regarding dogma. You'll find others who will be inspired by the chance for activism, by the openness, by the genuine compassion that can be found within most congregations.
Many people would be happy to donate their time and their money in order to be involved in such a setting, even during bleak economic times. Unfortunately, through our understandable distaste for evangelizing, we may have closed the door to even letting people know that we exist as a viable alternative to the more dogmatic creeds.