You seem to be thinking that manufacturing costs alone dictate the product cost. Demand and volume in circulation are also part of what determines costs, though. That is, your first assertion that they should be within cents of each other is clearly wrong.
It doesn't let us infer that there is a cheaper cost somewhere, it lets us infer that Amazon has a low confidence that someone will buy it. That or they have such a low inventory of it that they are not confident showing it on the buy box without more engagement from the users.
To be clear, I'm ok with the idea that this is getting investigated. I have low confidence of finding smoking gun reasons to punish sellers on this. I am far more confident that Amazon is optimizing to convert sales.