Good Afternoon Mike,
I have been trying to come up with a good way to make this work for everyone... I haven't even got to the point of figuring up the rental fees, I have some more research to do in that department. My initial thought was a monthly base rental fee and then I would stock the more common chemistry and then have a separate billing based on how much film was used. That way if someone only wanted to use some exotic process they could bring their own chemicals and wouldn't be paying for any of the chemicals that they weren't going to use.
Like I said, I'm still in the planning stages at this point so please feel free to make suggestions / comments, etc.