I hate to tell you all, misinformed folks (well actually I don't).. it's not expensive.. Like FIRST CLASS service, fantastic food 24/7 and all the amenities you could ever want (plus tax free booze/***s) for around a grand each for a week (or even less if you go Steerage) to New York - 6 days - you can fly back after staying in New York as well.
They do return trips at great value (Soton/NY/Soton) - when you take out the discount for non-flights for a very good standard cabin (i.e. Balcony etc.) a couple pay around £150 each per day - if you work out just what you're getting it is top-class value.