We have never priced a Towncar for this trip, but I expect you could do so on the major towncar sites (including that of our Sponsor, naturally). If you can fly into Melbourne (MLB - an adorable little airport), there is a shuttle of some sort, I am told (mentioned on the airport website), but I do not know the details.
Good luck! We love VB, and really ought to own points there, given that we've been once a year for the past few years.