The prices at hotels and in stores in PNG are not cheap, at least not compared to neighbouring Indonesia and probably other countries in the region. There is little domestic production, and many items are imported from China, Indonesia or Australia. Exchange rates vary a lot, so it's not really useful to give hotel prices here, but several hotels have webpages where you can check. In Port Moresby you may want to stay in "a good hotel" because of security (including the courtesy bus from and to the airport). In a place like Kavieng it is probably easier to follow the demands of your wallet, but even the cheapest room (fan but no aircon, mozzies in the room, baking hot in daytime) is not dirt cheap. I'm just saying this so you're prepared. As you have probably gathered from other stuff above, it's totally different as soon as you get out of town and hit the villages, you can live on a lot less then.