Australian citizens need only a Document of Identity, obtain-able from a Post Office. For other nationalities, a passport is required for entry and also for re-entry to your homeland.
The airfare to Norfolk Island is not cheap but, once you arrive, you will find other costs very reasonable.
Car hire is amongst the cheapest in the world. Petrol is dearer than on the mainland but a tankful will last you a week. All sporting activities are priced very reasonably and some are free. There are no madly expensive shows, probably the dearest being the Bounty Spectacular, for which you pay about $20 for a 1½ hour show with a large cast, staged on a replica of the famous ship. Freight and lighterage costs make certain items of packaged food expensive but meat is reasonable and eating out very affordable. There are dozens of clubs and casual eateries serving inexpensive light meals and prices even in the top restaurants are moderate. .If you are a fisherman, you will probably enjoy quite a few free meals. Cigarettes and tobacco are about $3.00 cheaper than on the mainland. And, of course, you'll find many bargains in the 77 tax-free shops.