Shop, shop, and shop.
Go to every site that you can (including the NCL site) and just fine the best bottom line deal that you can get. On cruise.com they have a "free" tour included in the price. I have talked to several companies and asked if they could make the deal a little bit sweeter. They might throw in some shipboard credit or knock a few more bucks off the price.
You also may want to consider booking a "guarantee" and you might get an upgrade for the same price.