I don't mean CPM prices but the value on your inventory page, we don't have anything like a RL economy, and most factions are not even business orientated so I'm confused as to what can make a difference.
In terms of stock value in the inventory, I believe it ties directly in with the number of stocks that have been released and how many (how large a percentage) you possess. That percentage is then calculated from the faction's overall value (meaning the combined total of their assets).
As Alex says, the value of each stock is based on the number of stocks released, and the value of the faction itself. THe value of your stocks is then based on that, and the number you have.