I honestly don't see the issue. It works how a market is supposed to work.

Player A works at Big Box Store A. Big Box Store A sells [Random Shirt] for 4.99.
Player B works at Big Box Store B. Big Box Store B sells [Random Shirt] for 4.49 to get more sales/business.
Player C works at Big Box Store C. They sell it for 3.99 to get even more sales/business.o make [Random Shirt], it cost 3.50 in materials.
Player C took the biggest hit, getting less per sale. But he likely will sell more in the long run.
Player A will get the most back per unit. But he may not sell as many unless the other suppliers run out.

Again, I don't see the issue. I'd rather know WHAT I'm paying up front then say a number based on past transactions... If a supplier things the item is worth so little, let them sell it for such.

Are any of them wrong? No. They value it how they feel is best for them.