I would suggest you dive Milne Bay region..direct flight to Alotoa from Moresby. Not just muck diving but ..everything! and there is a land based op there (cant remember the name sorry).
Things that will take you back to the stone age....ASK if anyone will take you to burial caves - but ask the dive op you are with to organise it, unfortunately you cant trust anyone in PNG unless you are paying them directly.
Trobriand Islands are magnificent....seeing someone pay for a wife with a pig is an awesome experience.
I believe there is an American guy living on the Sepik who does offer budget ''homestay'' but not sure of how to contact him.
Sepik..awesome, have only flown over it but WOW big big river!
Kokoda trail...again, you will have to pay for guards and make sure your guards and porters are ok....recently some aussie trekkers and their porters and guides were attacked with one guide killed from memory.
Again, sorry but you will spend a LOT in PNG but you wont regret it.
Timor.....ahh, I believe there is now a dive op there. I dived there in the 1990s while sailing through the area but was limited to locals pointing out where 'fish' were and had only a hookah set up onboard so I believe I probably missed the best bits - ditto Raja which was Irian Jaya then.
Have you thought about Alor? depending on timing..at times of the year the island is undiveable due to currents. Bangka in Sulawesi before the chinese mine moves in? Cubadak in Sumatra? Rote island is kicking off as a diving destination for those who want remote and no crowds.
There ARE no tourist shows in PNG - the country is not set up for tourists.......please please understand this is not a borneo headhunters tour stay in a longhouse overnight type place. Even the zoo had to be opened for us (i was there with a large companys CEO hence the VIP treatment) because the place is too bloody dangerous for tourists unless you have private security agents with you. There are NO shows, NO scenic areas you can go to by yourself and you cannot take PMVs (public transport). Do a LOT of reading up on what you are getting in for BEFORE you arrive in Moresby. This is not a country where you see what it was like 40,000 years ago, this is a country that IS 40,000 years ago.
I wish you the best but I wish you fully understand the reality of being in PNG
