In 4e, on the other hand, the fundamental (magic-item) economy makes no sense (out of the box). It costs no XP to create a magic item, but costs as much to make one as its market price! Of course, it's pretty easy to get around this if you consider the crafting ritual a quick, in-the-field ritual and assume that actual craftsmen use a more economically feasible one. But still, that's an assumption...
I think it's pretty explicit in the fluff text of the magic items that eg dwarven armour is not normally created by a Wizard snapping his fingers over a mundane suit of chain and spending the buy-price in residuum. It's normally laboriously crafted by dwarven master smiths.
Also, in the 4e DMG there's an explicit though optional 10-40% mark up over list price for items. So IMCs if you commission an item from a wizard you pay 10-40% over list. Likewise if a PC makes an item on commission, he can get paid 10-40% over list, which is almost pure profit. List price is used for the occasional existing item sold on the open market, or if you eg visit the dwarves to buy dwarven armour from them, or if a PC casts Enchant Item to make something.