What a product should cost depends on how much people are willing to pay for it. Whether a product should be allowed to exist depends on whether it's morally acceptable.
The issue with slaves, and products that pollute the environment or mistreat living things isn't how much they cost - it's that they exist at all.
I don't think the two are so easily separable. If you take for example, "a dozen eggs", most people would consider that an acceptable product. But if you said "a dozen eggs for ten cents", for those to be legitimate eggs, they must be stolen. If you could somehow inspect them and guarantee they were legitimate, I am sure plenty of people would accept those stolen eggs at that price, but their willingness to pay for it doesn't mean the existence of a market for "a dozen eggs for ten cents" is moral.
I'm reminded of how people would express outrage over products made in a low wage country being defective or toxic, and sometimes a response would be "well, people who demand ultra-cheap products deserve what they get". That's a denial of the fraudulent aspect of such a transaction, and the inability of the consumer to solve it.