is shipping cost paid by Amazon on various packages public knowledge?

I understand that Amazon is not likely to tell us how much their fulfillment center spends per item internally to find it in container, put it in the package and deliver to the mailbox or whatever their equivalent interface with the mail carrier. But, when they actually send the packages by mail or Fedex, presumably the price that they negotiated with these carriers could leak out and become public knowledge. Or maybe public knowledge within a small community of people who may care about such issues.

So does anybody have any idea about what these numbers might be or let’s say where they could be obtained by people inclined to find out?

Also, in terms of how their fulfillment centers (or any similar fulfillment centers) work, just wondering - at least qualitatively, is the typical true cost of the “handling” bigger or smaller than the price paid to the carrier for shipping? Just how efficient are fulfillment centers nowadays?

You can check out Fulfillment by Amazon. It’s a program that allows sellers to have Amazon warehouse and ship their goods.

Of course this wont give you the price Amazon pays, but it’ll give you a good idea of how good they’ve gotten at it. They will pick, pack and ship a one pound package for 90 cents.