On one hand, I feel your pain. On the other hand, cost and value are not the same thing, and so aren't value and market price.
If you do something and what you do costs much more than the market value of its output, make sure it's not your job. Hobbies usually fall in this category.
Right. The market price of a good is governed only by supply and demand. Sure, the cost it takes to produce the good influences its supply and demand, but in a capitalist society, only the market determines its price at the end of the day.
Let's forget the sunk cost for a minute. What happens if the price per item is less than the variable cost per item? Is that "unfair"? No, that's precisely how firms go out of business, when no one wants to pay (i.e. there is no demand) for the products they sell.
This is not an argument for plagiarism / piracy. Capitalist markets do need strong property ownership laws and enforcement.
In the same way that a liquid betting market, the price is a reasonable estimate for probability, in a any liquid market, the price is a reasonable estimate of value.
If you do something and what you do costs much more than the market value of its output, make sure it's not your job. Hobbies usually fall in this category.