Expensive public transportation in Brisbane

The public transportation is very expensive in Brisbane, but I guess it is more expensive to own a car. We have 2 cars in US and have no car in here now. We thought about riding a bike, but the slopes of those hills in every streets are 10 - 45 degree. It is not easy to bike in San Francisco city, I don't think it is easy in Brisbane.

Here is the information of public transportation in Brisbane area:
Translink bus zone map

South East Queensland zone map
Adult fares

When you travel in same zone, it is 1 zone travel. If you travel between zone 2 and 4, it is 2 zones travel. I am happy that at least the place we live and the university we go to are in the same zone.

The adult fare of a single trip for 1 zone travel = 2.4 AUD
The adult fare of a round trip for 1 zone travel = 4.8 AUD

For 1 zone travel:
monthly ticket: 76.8 AUD = 40 times with go card
3 month ticket: 211.2 AUD = 110 times with go card
6 month ticket: 403.2 AUD = 210 times with go card

We need to come to school 5 days per week, so it is 10 times per week. Should we use go card or just buy 3 month or 6 month ticket? It looks like that 3 or 6 month ticket can save us some bucks.