You could buy a three day dining package for each of you for $238.00 plus 20% gratuity ( $285.60), or $47.60 person per meal.
I will assume you're not heavy drinkers, and will work with 3 drinks per day per person. Bottled beer runs $6-7, cocktails $10-13. So let's average that out to $10 a drink. 7 days at 6 drinks per day equals 42 drinks for the week. 42x $10=$420.00.
So now you're looking at approx. $705.60 for drinks and dining.
When you book a cabin with free at sea, the cost is built into the fare.I think if you are happy letting NCL choose your cabin for you, you'll be ahead of the game. And if you go with free at sea, you 'll still have to pay an additional $277.20 charge for 20% gratuities on the drink package.
Hope my math is correct. If not, I'm more than certain someone will pick me up on it!!