They had to mention the $5000 per day so we would know what a good time they are having!
Their cabin is one of the upper suites. It may be comparable to a Junior Penthouse - and I assume that fare is for two people in the cabin. The lesser suites on Splendor are more reasonable. It's hard to compare because a lot of their fares include business class airfare.
Still, it's looking like $1000 per day per person is kind of normal for a luxury line these days. You can easily fork over that kind of dough even on Viking Ocean.