What Merrie was trying to say is - if a cabin costs $4000 per person, double occupancy, then the price for a single would be $7000. $4000 + (75% of $4000 =) $3000.
So a single pays 175% of the "per person " fare.
Still outrageous when lines like Silversea start at 110%, HAL 150%, RSSC 110-150%,
But almost all charge 200% for their premium cabins.
Your only hope is to sign up for a share program like HAL has, and hope that they don't match you, in which case you get the cabin to yourself at the cheap rate.