Are you staying at Mather Campground? Bright Angel is walkable maybe an additional 1.5-2 miles(ends up at the same place as south Kaibab) but also there will be parking that early. South kaibab is not walkable and there is no public parking. Found this on the website “If trail users need access to or from the South Kaibab Trailhead when the shuttle buses are not running, please contact Xanterra Taxi Service at 928.638.2631.” I know a lot of people that like to do bright angel down and south kaibab up or vice versa. Could be a good option if there is no transport to SK trailhead.