Have I got a hearing aid for you

I imagine there are.

I don't know about kickbacks & whatnot in the U.S., but there is definitely room for undercutting established manufacturers. What I would call a "decent" pair of hearing aids -- the kind of thing that might have been top of the line 3-5 years ago -- will run perhaps $5,000. Top of the line will be perhaps $7,000-10,000 for a pair.

So what do we have to come up with to make a hearing aid?

Materials: we need a custom enclosure (the in-the-ear part of a hearing aid is made from a mold of the user's ear). For an in-the-ear aid, this enclosure contains everything. For a behind-the-ear style, it will contain only a speaker and be connected to the main unit via a wire[1]. For both kinds, the main unit also needs 1 or more microphones, spots for push button(s) and a battery case, and the computer that runs it all. Also a 2-way radio data link for configuration & software update; perhaps for talking to a handheld remote control as well.

Is there an off-the-shelf computer that would fit inside a hearing aid? Something like an Arduino is much too large.

Then the software has to be written.

And, as with anything in the health-care industry, there are liability issues, and the hurdles to jump: regulations, licensing, hiring the necessary expertise, and mountains of paperwork. There is probably a minefield full of patents to dodge, too.

Off the top of my head, I don't see any reason why a resourceful group of people couldn't come up with a top-of-the-line hearing aid that sold for about $1,000 for a pair and still allowed for a profit. Connecting with customers would probably be the really difficult problem.

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[1] This seems to be the usual design these days. Older behind-the-ear aids put the speaker in the main unit and had it play sound through a tube connected to the earpiece, which was just a custom-shaped piece of plastic with a hole in it.