It varies by each operating certificate. Some airlines can depart with RVR as low as 300ft if it is approved for the specific airport. There are certain requirements to allow this such as visible runway centerline markings AND lights as well as operable RVR reporting and runway edge lights. Others as low as 600ft. However some airports require higher mins such as 1600RVR for airport specific reasons. It goes the same for arrivals. With the proper equipment and training a crew could land in 0/0.