On a temporary visa you would be covered by the reciprocal arrangement but it would be for necessary medical cover only - like if you had appendicitis or something. They certainly expect you to be responsible for your medical cover and to have private medical (your sponsor is supposed to be responsible for those costs but I think some of them neglect to factor that in to their calculations!) You can get a good idea of what it will cost you from
Private Health Insurance Australia - iSelect Ours costs about $240 a month with HCF for top hospital with excess.
Dentists - everyone pays for them and part of their payment would be reimbursed from your private insurance - it's an "extras" option on the policy and also covers therapies, glasses etc. Otherwise you bear the whole cost yourself.