Yes, good point about Costco (or any provider, really) not willing to give it a try because there is is no loss of hearing. I hadn’t thought that far ahead and you are right, they aren’t going to treat a non-hearing loss.
Let me go further, to the spirit of my suggestion:
We all get old. I am 77. As we age we encounter physical problems. We go to the doctor. Mostly we get answers based in science or proven experience. Now and then - and anybody who is old certainly understands this - we encounter problems that have no good solution in conventional medicine. At this point, what do we do?
Some of my friends simply stop. And suffer. They have placed all their eggs in the conventional medicine basket. If their doctor (and referred specialists) don’t have an answer, or if the recommended answer doesn’t work, they seem to presume that there is no help and they don’t pursue other options.
I don’t stop. I look elsewhere. I have back problems, I have diverticulitis, I have these and other maladies that evade conventional medicine. What am I to do? What I do is look to what others in my situation have tried, or what I can think of that might relate. And often I have found relief in alternate forms of therapy such as chiropractic or acupuncture or dietary changes, none of which are explained by science or conventional medicine. I sometimes find answers in folk medicine. Or in things that I just dream up myself. And I have virtually never failed to find some sort of relief, so long as I just keep trying things that make some sense to me. I am a retired engineer. Engineers solve problems, it’s what we do. And when the going gets tough we try anything and everything that might have a shot.
In my younger years, due to my technical background and faith that conventional medicine can solve all problems, I wanted and expected a differential diagnosis and a double-blind tested solution to all my problems. Well guess what? I learned over the years that modern medicine doesn’t have all the answers. Now I’m not fussy about where I find relief, because I’ve experienced too many problems over the course of a long life that don’t have double-blinded answers. I don’t care anymore about double-blinded. I don’t care if it’s a placebo effect. I just want relief, so I keep trying one thing after another until I find something that helps.
So, it’s in this spirit that I offer an idea in response to the OP. This person has tried the conventional means and has come up empty and is suffering and truly desperate. There seem to be no red flags from his providers that would warn him/her of something dire, and his providers aren’t providing a solution or a referral. So… time to start trying anything that might have a shot, if you ask me. One thing I might try is, to find a hearing aid someplace, and stick in in my ear, and turn the volume down, and see if anything changes. It probably won’t fix the problem, but it sure wont hurt anything to try. And there is a certain amount of logic to it: These devices seem to process every sound in some way - what comes out of a hearing aid, in my experience, is never what went in to it. So, what’s to lose by trying?