What is the value of a soul? Is it effected by population? Is there soul inflation? What has a soul? Do the souls of different creatures have different values? Are they traded like commodity, or are they more like fine art, or something real estate?
Religions can vary a bit on what a soul is, and what might have one. Assuming humanity as a whole has souls, did any of our extinct relatives? Neanderthals could and did breed with humans, and had fertile offspring. So, I guess they had souls too. This leads me to ask, where the cut off for souls? What about homo erectus? Or homo hablis? Or any of the Australopithecus? The great apes? Gibbons? And are they worth the same as a modern human's? No way to know.
Does the value of the average soul go down over time? Population goes up overtime, so therefore the rarity of souls goes down. Does the rarity effect the value? When the world population was only a few hundred-thousand was a souls worth more than now when the population is over seven billion? Does that mean that over time the selling of souls has become a buyer's market?