WikiVoyage has a fairly good section on getting from Brisbane Airport to the CBD, including things like the AirTrain and cheaper alternatives. For a daytime arrival, it looks to have everything covered!
Unfortunately for me, it looks like following a change of plans that I might be getting into Brisbane at a little after 11pm, so my previous research is of no help. I probably won't have cleared immigration and customs until after midnight, so the airtrain is out (22:02 from International looks to be the last service in the week), and I fear the free bus to the Airport Village may well have stopped long before too.
Are there any cheap ways into the CBD late at night from the airport? Or am I going to have to hope I can find enough people to share a taxi with to make it a moderately sensible price?