First a disclaimer: in my household we have to buy high-powered BTE every 4 years or so, so I am close to the subject.
So, let's see:
First off, we should discern between medically useful features and convenience features, realizing that there is no sharp line between them. We buy fully digital, high-power BTE aids with complex programming capabilities, and those aids (which are pretty much top of the line when it comes to their intended function, i.e., help the wearer hear as well as possible) do not cost $8000 a pair. Not even close - try about half that. We forego bluetooth (but not FM), a gazillion programs, microscopic sizes the size of a fly head (not available of you are profoundly deaf anyways) and God knows what else for pooling our resources (= $$$) into maximum power and amplification/programming capabilities. I suppose we get the Ferrari, not the Lamborghini, if you wish. A lot of cost goes into stuff you may not need (but may want just as much as you want an iPad you probably don't need).
Second, there is significant markup when you buy retail - because you cannot just buy the aid, you also buy the service to have the aid fitted to you. That cost is never broken out, but you would be surprised how much your audiologist might charge you there. Definitely an eye opener. Seems a bit like a cartel, really.
Third, I will give hearing aid companies that they (at least some of them) do a lot of R&D. As I said, we need to get cutting edge aids, and so far I have seen significant improvements over the years. Now that may change (soon??), thoguh I have to say there is still plenty to be done to make BTE aids better performing. Same goes for convenience, but I do not want to pay that price.
Fourth, there seems to be an uptick in insurance companies to pay for aids (ours has not in the past). At least for children and young adults I think it is flat out a crime not to pay for aids.
Fifth: If you really want to be upset you should ask what the production cost of those aids is, and what the resulting markup is. Would want you to become a maker of BTE aids in an instant. But, fo course, that is where capitalism sort of fails: this is a very high entry market. To play, you need to invest a lot of money and a lot of time. And once you made it, you can fleece (ahem, charge) your customers accordingly.
So, are they too expensive? A lot of them are, but if you are smart about it, you can save thousands of dollars or euros (the story is identical in Europe) and still get the aid you want with full warranty. BTW, I heard they are (much) cheaper in Asia.
I do agree,however, in that I wonder whether the "digital gains" are now starting to peter off, and the main advances will be in software only. Well, I suppose I will find out again next year ...