From Tullamarine Airport, the cheapest way to get to the CBD is by the SkyBus. A single one-way ticket costs $18.75 and a return is $36.
The SkyBus runs approximately every 10 to 15 minutes, 24 hours a day, every day of the week, including public holidays, and will take you to Southern Cross Station. From there, you are able to catch trams, trains, a taxi or Uber to your accommodation. No bookings are required for the SkyBus. The StarBus is also an affordable way of getting to your destination from the airport. It is a shuttle bus that will deliver you directly to your door in certain suburbs (including Carlton, North Melbourne and Parkville). Tickets range from $20-$27 per person and bookings are required.
If you would prefer to go directly to your accommodation, there are many taxi ranks located around the airport.
Alternatively, Uber is also available from the airport. There are two Uber Pickup Zones – one for Terminals 1, 2 and 3, and another for Terminal 4 which is located on level 2 of the Terminal 4 carpark. Once you have made your way to the Pickup Zone you can request your Uber and be on your way.