I can sympathise because you have only been here a few months, so may not have been aware of the costs of dentists and that taking out 'extras' cover is a good idea (if it suits your circumstances).
This posting will hopefully prove as a reminder to others coming over of the potential costs.
We were aware that dental was expensive in Australia and before we left the UK went to our dentist and both had check ups and cleans. We have extras cover through Medibank and we always get our money back, usually we get double the amount of the premium and that is before anything major goes wrong.
I would say the costs quoted seem about right. I have a front tooth that is a crown and when it needs replacing I have been quoted by 2 dentists around $1200, but with our medibank policy I would get around $840 back.
Under our policy we are also entitled to a free check up and clean each year. We went this week and if we had to pay for this it would have cost us $163.
I suppose the other thing to mention is ambulance cover, this is another insurance that people think they will never need until something happens and they get a bill for $800! The 'extras' cover usually includes ambulance cover.