If you are wanting to go to KI & driving your own car over then checkout www.sealink.com.au Ferry Leaves @ about 6:am and probably need to allow about 2 hours to get down there depending on where you are staying plus check in & loading time otherwise there is a bus and tours that are available. A friend of mine went over by ferry I think he left about 4am but he's about 45mins the other side of Adelaide.
About $180 - $200's return with your car. Also check out RAA SA's Equivelant of RACQ if your a member of RACQ you may be eligable for special rates if booked through RAA or RACQ.

Yes the scenery is great every rock over there is over photograghed but if you get there have a go.