Pacific isls how to get around?

Hi,

Im planning a trip to PNG and some pacific islands. I know you can take the plane to go from one to another islands, but its rather expensive. Id like to see the prices from virginblue etc but I cant enter a 'right' date? Can someone help me with this, pls?
I also heard you can take a vessel from one to another island. Are there vessels that go on regular base? Could you give some routes (and prices). Is I have plenty of time, I can stay weeks on the same island. Normally I want to go back to N-Zealand and from thereon i take a plane to Chile. Or can I visit french polynesia (eg) and take a cargo ship to Panama? Is this possible (theoretical and practical)? How can I arrange a 'ride' with a cargo (price)?
Or any other suggestions would be welcome.
Thank you very much
G

Basically, the ship passages are from island to island within the same country - there is nothing on a regular or commercial basis from one country to another. You can fly from Port Moresby to Honiara in Solomon Islands, and from Honiara to Fiji, Vanuatu and Nauru.
Pacific Blue (Virgin) has regular flights from Brisbane to Honiara on Tuesdays and Thursdays, I am not sure which days it flies to anywhere else.

For a PNG trip, I'd extend only to those island groups mentioned above. You really do need to fly between countries, e.g. no freighters will take you from Tahiti to Panama, etc.

You can route yourself via NZ to Tahiti to Easter Island to Chile, if you use Star Alliance members.