shannons are usually the cheapest but you have to be in a car "club" and over 25 (sau counts and you can be under 25)
i think they are underwritten by aami like justcar so the price should be the same
i'm with justcar and its about 1,400 / year paying by the month (~$130/month) (20 y/o, rating 3ish, no claims, couple of points lost)
with justcar, you have to have an aust standards immobiliser that is installed by a pro