Read my next post pls.
Also, since you want to open the can of worms and since I'm feeling bored. Here goes...
In 2013( I think) 1964 ears (64 audio) was approached by this company called asius technology, offering them a new technology to relieve pressure and improve sound. It is called Adel. The Adel modules function by having a movable membrane in a vented module. The membrane absorbs pneumatic pressure. However, the module changed the sound too much and the new line has to be retuned around the new sound. Fast forward to 2016 and a disagreement over QC lead 64 to split with asius. They now had to develop their own modules that sound the same at least. So they developed apex which does not have a membrane but instead has laser precision ports to allow pressure release.
As for the exorbitant costs. U can attribute that to rnd today.
Traditionally, manufacturers of ba based iems could tweak them by adjusting: the driver type, the number of drivers, the crossovers and length, material of sound tubes and placement of filters. While dynamic drivers experiment on the airflow of the housing, the magnets, and the coating of the diaphragm. ( I cannot comment too much on DD development).
For ba, the traditional means have practically reached their limits for off the shelf bas. Now, they have to develop their own bas which is not cheap. Then, they have to push the limits further pioneering new crossover technology of fine-tuning the response curve or creating new technologies like resonance chambers.
I think the bulk of the cost would be the development of new bas. For some companies, manpower costs can be expensive, especially to assemble custom iems