The Cineplex at South Bank on Grey Street is by and far the cheapest cinema in Brisbane. With movies starting at around $8 for 2D and $10 for 3D (+ $1 for the glasses) we tend to go there all the time. I haven't been there on their cheap Tuesdays, but I think for $8 you get a movie, popcorn and drink deal.
While most of their theatres are fairly small I tend to attend movies there when they are in cinema 5, which is an ex-IMAX theatre and has a very wide screen.
I have to admit the seats at places like Myers Centre are wider and generally nicer, there is no fault I can find about the South Bank Cineplex, other than it can become extremely busy on weekends and school holidays, but it is a great option on weeknights.
Let's not forget that it is in South Bank, so lots of different choices for restaurants, coffee and drinks before and after the movie and at night or weekends you can park down the street for free if you don't mind walking a little while and there are 3 hour free parking options for people going to see a movie.
One last thing, we know that cinemas actually make all their profitability from the concession stand, not the tickets anyway, so why do they need to charge so much for tickets? Go to the Myer Centre theatre and there is hardly anyone there, not sure how they make money.