The main point of my post was questioning your assertion that Carindale and Chermside are outer suburbs.briztoon, the point of my post was it is far more economical to run buses short distances. Also was a reply to Coach transport.
Nerang to Carrara and return you may be able to use at a wild guess 12 or so buses.
They just keep doing the loop of 2km each way, 2 hours before and 1 hour after the game.
They also run shuttle buses from Broadbeach South Station near Pacific Fair Shopping Centre being an 8 km journey.
That route may require more buses especially after the game.
They only have these two start/return points. Also similar to Brisbane they have free transport on all Surfside Buses and Light Rail.
The Gabba similarly run City only shuttle buses that also do the loop.
This is way more economical than putting on special buses that go to and from Chermside and Carindale.
But the Lions and Broncos know this has to be done to get the crowds to and from the games in a large city with both venues just outside the CBD. So, they pay whatever the costs are and pass those costs on.
Coaches are run by private companies and don't have anywhere near the number of buses or drivers compared to council buses.
No doubt coaches would be faster than rail from Carindale & Garden City as you mentioned.
But people live all over Brisbane and i can't see the Lions choosing a couple of southside spots to run free buses to Carrara.
So, people would have to pay extra to go by coach from any chosen Brisbane location in my opinion.
If there was demand for paid coaches, you could do it but i don't think there would be.
However, i recon a couple of paid coaches could go from Lions Springwood social club though.
If you think coaches are the way to go transport wise to Carrara by all means, please make a case to justify that choice.
If you are only thinking of a small number say 4 coaches each game that's a little different. Someone would still have to pay though.
A quick google search on Brisbane based coaches, they carry a capacity of between 50-60 people.