Simple.
The average player might not have the wits to outsmart Albert Einstein when it comes to physics (Martin doesn't play
) but he does understand when he is being given a "bad deal".I mean, if the idea behind the huge prices of NPCs is to take money out of game.. it's as upside down as it can possibly be. I always thought that it was to encourage PtP trade. Anyways. What will happen is, that players will not *buy* these expensive items if they will get away with it. If the item is "fun" or "time saving" item (read: Portal) then he will do without. I don't really understand whose idea the increase of price was, but personally that has resulted in far less portals being bought. While per unit, a lot more money is being taken out, the total amount is substantially less due to the lessening use.
What you need, is something that benefits the player. A fair trade. Something that you have a monopoly on and that is useful enough to justify the moderate amount of money they have to spend on it. What would be even more useful was, if it was 1.) Consumable under certain circumstances (not necessarily like a potion, but in way that requires the purchase of a new one or can be lost) 2.) That gives the using players a slight, continuous advantage and thus encourages others to buy it as well.
A horse.
