Some informative reading here:
http://www.bicycle-stuff.com/main/director/index.htm
Also look on some of the past rides and read the reviews, may be informative.
Note that this is north Texas related, and some things may vary regionally.
On the normal pay-your-$30-and-ride events around here, most of them are organized by the charity in question, which gives them a ready-made base of volunteers to run the event. One local ride is organized by a bike club. A couple of local rides are organized by a professional, although they may benefit a local charity. (Some of the volunteers in that case are peple doing their mandatory "community service".)
It is possible to lose money on an endeavor like this, or to lose money for a year or two until you build up ridership, etc. So it helps if it's not a shoestring operation. You'll have upfront costs like insurance and traffic control and t-shirts, and then if it's pouring rain and nobody comes, you have problems.
It might be helpful to contact some ride organizers in the area and get their insight if possible.