I have never sailed on Norwegian, but their price for wine must be about the same as other cruiselines.
I find that the wine on board is priced fairly reasonable and it sure beats having to carry it onboard.
Carnival Liberty New Year's Eve 2007
Liberty of the Seas 5/2008+11/2009
Allure 1/16/ 2011
Independence of the Seas 12/29/2013 Top-notch!