I have looked into opening a co-op just recently. There is a moratorium on opening one that was just extended until next May. What you have to do is buy somebody elses license which starts at $50,000 (so much for capitalism)

The DEA has no interest whatsoever in busting the co-op owners, in fact they usually do nothing but trash the place and intimidate. I know a few that have been busted and they don't even take their product or cash most of the time. They are looking for untaxed cash and guns for the most part. I don't know any dispensary owners that have been prosecuted so far. The Venice dispensary operates across from the Venice Police Dept on the boardwalk. It's brilliant...
Jerry Brown is trying to pass legislation that all dispensaries operate as a non profit organization which means you would need a 501C I believe it's called to operate a co-op. Good luck man...imp: