Having lived and worked 15 years in PNG though I concur with the initial review .I feel its painted far worse than it really is.Common sense should be used,but I have travelled in most provinces and no problems.I would avoid Lae most probably as being the most risky.
Guest houses are cheaper and usually safe.But you may get chatted up a lot(good for the ego) Remember AIDs is common so behave.Learn a littrle Pidgin and travel with care.Women ,never travel alone! Be cauitious at night when out,very cautious.
I have an advantage as I am married to a PNG lady .
Try Goroka for the September sing-sing.Kimbe for the diving and if driving in the Highlands don't stop if you hit a pig.