If you are intending to camp during the Summer School Holidays
There will be almost nowhere "Quiet" near a beach and many (commercial) places already booked out
Even worse on a Weekend and forget Australia Day long weekend.
You could aim for 2+hrs from Melbourne to the East or West.
2 Hrs west (of Geelong) gets you the great Ocean Rd /Otways/ Warrnambool, which are major holiday destinations.
To get anything remotely quiet try 3 - 4 hours west, Portland and beyond
2 Hrs East/ Sth East gets you Wilsons Prom/ 90 Mile Beach / Lakes Entrance, which are major holiday destinations.
To get anything remotely quiet try 3 - 4 hours East, Orbost and Beyond