The open-mic that I used to help run was an adjunct to a non-profit cooperative avant-garde art gallery. The gallery had more space than it needed and they let us use the back room for music every Friday night. The format was open-mic with the occasional invited guest performer. On regular open-mic nights, we charged one dollar admission and the proceeds went to the gallery. On guest performer nights we charged more and the guest got all of it. Four of us rotated the hosting and sound board responsibilities. It would probably still be going on today but for the building deteriorating to the point that the owner was forced to do extensive repairs and remodelling and had to increase the rent to more than the gallery could afford.

If something similar exists in your town it might be worth checking into. Affiliation with any existing organization, even a church, will give you a pre-existing membership list to whom you can send promotional fliers. BTW, if you do go the church basement route, Unitarians are historically the most coffee-house receptive bunch.

Bruce