We were on the Norwegian Sun a couple of years ago. Really had a good time. Like most cruislines, you can expect to pay extra for pop and drinks, gambling, BINGO, sounvenirs, photos from ship's photographer, shore excursions, tips, and if you go to any of the restaurants that have a cover charge. The two main dining rooms are free, the buffet, Pacific Heights, and I think someone said Los Rambles or something like that is free. Any spa treatments you will have to pay for. So it depends on what you plan to do. We are not drinkers or gamblers. We play some BINGO so our spending is relatively less than most.
pop is about $1.75 a can and other drinks vary. The tip that is added on your charge will be $70 per person. The cover charges in the restarants vary between $10-15 per person I think. The Ginza Restarant with the teppenyaki is higher as you pay a-la-carte I think there.
Hope this helps.