NCl wave 2015 promotions give european cruise 2 of the 3 offers.
OBC (on board credit)
Ultimate dining (Most charge restaurant every night)
Ultimate beverage (a large range of drinks)http://www.ncl.com/promo/wave15
The best prices are on the Jade from Rome and the Spirit from Barcelona fropm around £400pp.
full list of cruiseshttp://www.ncl.com/vacations/europe-cruises?destinations=4294934557
Booking can be done direct on NCL.com or through a US travel agent. or by phoning NCL in the US.
Tips/gratuities are $12pppd
Flights were available from around £80 uk airport and there are some avios available
I also found some BA LHR for <£150