Dual training RA-Aus fees around Melbourne can be found between $200 - $250 per hour with solo fees perhaps $60-$70 less. You'll also need to join RA-Aus.
The minimum hours legally are 20 hours (mix of solo and dual hours) for the basic certificate, however it often takes more. Nav endorsement is an additional 10 hours.
Solo can potentially be achieved in around 10 hours (but this is not a certificate or licence, just a milestone).
There are training organisations offering solo packages with lots of hype and alleged inclusions... but there's little point in these; just go with the hourly rate that you like and a school that will meet your needs and take it from there.
PS: If you are an overseas visitor, make sure you don't get the RA-Aus certificate and the CASA RPL confused - they are a different beast. I wouldn't be too concerned about the weather, although November can be a windy month in Victoria.