Most consoles sell at a loss, that is the price for a profit, including the cost of windows (while steambox will be linux), and at a manufacturing scale that is probably 1/500th or less of what Valve will be contracting.

Not to mention that may very well not be "the" steambox, as apparently Valve has said they will have multiple prototypes from multiple manufacturers.

Xi3 also offers the entry level X5A, which is priced at $499