Please advise if this doesn't belong here, but a neat workaround if you need to park at Melb airport to send someone off or meet someone arriving.
Drive up rates at T123 are $12 for the first hour and $24 for 90 mins. But if you book online you get a grace period of 1 hour either side of your booked entry and exit times. So say you book 3pm to 3.30pm. You can enter as early as 2pm and exit up until 4.30pm without incurring additional charges. All for $7. Same applies to T4.
Edit 22/1: T1, T2, T3 now $8 (Up from $7).