It's subjective, but that doesn't make it nonexistent. I pay $10/mo. for Spotify. I'm happy with that. I think I get great value for that money spent. If someone came out with an $8/month streaming service, I'd scrutinize it fairly closely before contemplating switching.
Are you actually saying that you would refuse to use a service (all other things being equal) that was $8/month because $10/month is what you think is "fair?"
If so, I'd mark that behavior as strange, and not actually evidence of the existence of a "fair price." There's no way this behavior is typical.
If what you're saying is that you'd assume a price lower than $10/month would have other, unseen problems, then:
1) You're not referring to a "fair price" but instead a believable price, which is a compromise between what you want to pay (which is nothing) and what you estimate to be the price of delivery, and the odds with that price in mind that what you receive will be adulterated/lower-quality than advertised.
2) How is $10/month fair? No wonder musicians don't make any money.
It's subjective, but that doesn't make it nonexistent. I pay $10/mo. for Spotify. I'm happy with that. I think I get great value for that money spent. If someone came out with an $8/month streaming service, I'd scrutinize it fairly closely before contemplating switching.