Imagine that the supplier of the parts (cacao) of the manufactured product didn’t have to pay anyone to make the parts. Imagine how low the price for the parts would be for the manufacturer (the chocolate maker), and how little it would cost you to buy the finished item. Like chocolate.
The child slaves (the no-pay part!) harvest the the cacao – some say coco - pods and then the suppliers (slavers, say) sell the cacao, the key ingredient in chocolate, to the chocolate makers. You then get chocolate that you are familiar with at a low price.
When someone is being paid fairly, the price for that chocolate without slavery is necessarily going to be more. We know it is worth it.
Investigating the Dark Side of the World's Most Seductive Sweet
Carol Off's excellent book explaining chocolate and slavery, how it started and why it hasn't been stopped.