Back when the KS2 caverns KS started many people commented on how much more expensive it was than KS1 dungeons, so I am not surprised that the same thing is happening now from KS5 to KS6.
Cavern sculpts are way move detailed with nooks and spikes so it takes what I believe were called sliding molds back in KS2 plus some of these KS6 peices a huge.
If you are looking for table coverage in caverns then KS2 sets are the way to go. I love my KS2 caverns but I am ready to get some KS6 caverns to add more elevation, variety and a more organic lay out.
I could just get a couple encounter sets and call it good but I really like many of the KS6 peices so I expect to get more than a few by the end of the Pledge Manager.