The Rohloff is expensive due to multiple factors. It is made in Germany in limited numbers and assembled by hand per a video that has been linked to on BF IIRC. The Schlumpf is made in Switzerland which has even higher labor rates than Germany. Even the Shimano 8 speed hub, made in much larger quantities in a lower lbor rate setting and with more automated assembly, does not meet the $200 price point mentioned. A lot of small precision parts go into a 8 speed or more complex IGH.

Commercial derailleur drivetrain full chaincases are not available for several reasons IMO. They would need to be large and due to dimensional differences between various frames it would be difficult to make one that fit more than one model of bike and chainring/cassette combination.