My enriched economics textbook asks what would the supply and deman for organ transplants look like. I think law and economics are ways of looking at the same thing. This is how I answered the assignment. If the "floor" makes it illegal to sell organs, but legal to be a donor, then the floor would be set at zero. From the graph, 100 organ donors would be willing to supply kidneys, lungs, livers, and other organs. The higher equilibrium suggests that there is a black market for these organs. My textbook has a case where the price of a liver reached $5 million on Ebay before the illegal online auction was shut down.
In Made to Stick, the authors tell a tale of a kidney heist. Chip and Dan Heath argue that kidney harvesting is an urban myth. Econ 101 implies that there is an equilibrium for illegal organs.