I always use the SkyBus shuttle service from the airport to the city. It operates 24 hours a day.
You can arrange an additional hotel shuttle from the terminus at Southern Cross station (in the city) for no extra charge.
http://www.skybus.com.au/hotel-transfer-service/ about 7 years ago
Alternatively if you can get a Maxi cab that can fit 6 people each car. To get from tullamarine to Thierry st should cost about $50-$60 in a cab. So, that times 2 cabs = $120 approx.
compared that to skybus at $12each person one way = 12 x$12 = $144 - cab can still be cheaper and more convenient way about 7 years ago