first you become a part of the co-op. you need proper paper work showing that you are legal to have and or grow medical marijuana. once you do that the rest falls in place.
some co-ops have contracts, others don't. it just depends.
prices also depend on if it is grown indoors/outdoors/greenhouse. is it top shelf? the co op reimburses you the cost it took to grow the medicine. some co ops will do a 1099, some are consignment only. you just need to do research. they can't talk on the phone but some have websites you may find your answers there. or just call one up and ask when they are seeing vendors. go in fill out your paper work to become part of co op and then you can ask any questions you have. clubs, co op, they are looking for good medicine for their patients. if you grow good meds then they will want to talk to you.
the thin line i am not totally sure of here, (call norml) is transportation. so do your homework before you venture out, you don't want to get into trouble
P.S. most clubs won't reimburse for anything less than a pound.