Even if someone at Costco who "mattered" saw your complaint, how would they know you aren't a desperate, narcotic seeking junkie determined to bypass their rules? The answer is, they wouldn't. So I doubt it would get anywhere. It's an unfortunate fact that all of us need medications that cost a lot, or too much.
This discussion reminds me of a high school classmate of mine who, as a medical doctor specializing in internal medicine, ended up being investigated by the DEA for overprescribing narcotic meds to his patients. This investigation came after he prescribed narcotic painkillers to a patient of his who notably lived 180 miles away from his office and later died of an overdose of meds he had prescribed. Apparently word was out on the street about this guy, for the patient who OD'd to know where to go. The DEA actually accessed some database that showed he had prescribed the 7th highest amount of pain meds in my State during a specified period of time, so he had been on their "watch list" of doctors who were giving out the narcotic meds like candy. When the investigation revealed he had prescribed meds and billed treatments to Medicare for patients who died or did not exist, it was basically over. He pled out to all charges and is now serving time in federal prison. The moral of the story is this drug epidemic is a HUGE problem, and because it's being coupled with Medicare fraud it is on the radar of both DEA and the FBI. I also have a high school classmate who works for the FBI in the Medicare fraud unit, so I hear a lot about the general concerns of law enforcement in this field.
It's sad that it effects all of us in this way, but this narcotic drug epidemic is a huge problem that we have to do a better job with as a country and a society.