People outside Australia don't appreciate how large the Pacific Ocean is. Stringing cables across it is monsterously expensive, plus US carriers charge us for traffic we send to them but don't credit us for traffic they send to us. Also, there only is one decent cable into Australia from the US, and every time someone needs to build a new one the outlay is approximately AUD1bn.
To give you an idea of the costs businesses are paying, we sell an unlimited 2M connection for AUD12,000/month RRP. On our metered connections, 1GB downloaded from overseas costs you around AUD110-130. So getting a 512K connection and 3GB of downloads for AUD95/month is really the bargain of the century in Australian terms.
All that said, most of the prices being charged today are really reflective of how things were before the new Southern Cross cable - and since people are used to that being the way it is, and there's no real choice - guess what, that's what you get charged.
Still, AUD25/mo for unlimited downloads is not economically viable, I can tell you. It costs even those that own the cable something like 3-5c per MB downloaded, and they charge about 11-13c - about standard margin. It doesn't take all that many 3-5c + support and equipment costs to make up $25.
