R.,
I am the director of a co-op just north of Cincinnati. We have a website www.masoncoop.org with a lot of our forms and information available on it. Also, my friend has written a book about starting homeschool co-ops that is very helpful. http://homeschoolcpa.com/
We meet once a week on Fridays (any more and you interfere with getting lessons done at home.) We have 2 semesters that are 14 weeks long. Most of our teachers are our own parents (we actually have a dad who teaches chemistry, taking Friday mornings off to do it.) We have some teachers (art, Spanish and guitar) who are professionals that our parents pay directly. We have about 140 students from the nursery through 12th grade who rotate classes in 3 hours.
We charge $75/family/semester with a discount for teaching a class. This, along with the Kroger card and Box Tops for Education, covers our rent at the church and class expenses.
I hope this helps. Feel free to contact me again if you have any specific questions after checking out the website.
M.