Me and a bunch of mates did this last September. My mate had a 33 (rb25) and that only took $140 of 98 round trip...
Depends on how much of a lead foot you are, too! We didn't drive around much in Melbourne, though - basically dumped the car at the hotel and went in search of random side-street clubs!!
Melbournes side-street clubs ftw!! They're crazy.