Not many people who browse this forum have experiences with ANU. As for the combined comp sci and economics degree, I'll give my opinions, since I did 2.5 years of economics at USYD and completing a comp sci minor.
Firstly, I don't believe the two subject areas are complimentary at all. In your future career, if you get hired for economics, you're not going to be using your comp sci skills, and visa versa. They use very different skills, and it's unlikely you'll be able to combine them in any meaningful way in the workplace.
In terms of employment, it's easier to find a job as a programmer having graduated from comp sci, than it is to find a job as an economist having graduated from economics. There's also an interesting belief that graduating from economics can get you into roles in finance/banking/commerce. This is not generally true. Economics isn't a very practical discipline. Even in an economics role, you'll be generally relying on statistical tools than anything. That said, if you're interested in becoming an economics researcher in academia, then go for it.