Thanks to all the off-list responses. Really insightful.
Short summary :
1. IP back to the US is between $300 and $700 (AU) per
month per Mbps.
2. Difficult to peer directly with the 4 big ISPs. Easier
(relatively speaking) to find multilaretal peering with
the 600-odd smaller ISPs.
3. Equinix Sydney comes highly recommended (used to be
Pihana).
I will happily mail a digest of all responses to anyone
interested in the details or horror stories.
Thanks again !