Thanks John for your answer. I am looking at the Norwegian Fiords cruise with the Queen Elizabeth on August 11th, 2017. Nine nights from Southhampton.On the UK website, that cruise is showing the following prices:
Oceanview per person is US 1199. This means for two people is about US 2.500 including taxes and fees. But if booking solo, it comes a price of almost US 4.500 for same ocean view category including taxes and fees.
Cheapest Oceanview (Double): £1349 ( $1713) per person, i.e. £2698 ( $3426 ) per cabin
Cheapest Oceanview (Sole): £2229 ( $2808 ) per person, i.e. £2229 ( $2808 ) per cabin
So that's a 165% solo increase.
Therefor your US figures are very different from the UK figures for a solo occupancy ( $2808 v $4500 ).