Intel does the math for manufacturers.
The brief word on the street was that ODMs/OEMs were having trouble making Ultrabooks (essentially laptops with a form like a MacBook Air) for under $1,000. Then a report popped up of Acer's offering that should creep in at $768 to $960, helping to put to rest the fears of a ballooned budget.
According to Digitimes, Intel has put together a reference design and bill of materials that range from $475 to $710. Mind you, that's the just the material cost, so the final product will definitely reflect further value-added cost on top.
The Taiwanese publication details that the 0.8-inch (21 mm) notebooks have a BOM of $475 to $650 and the 0.7-inch (18 mm) design has one $493 to $710.
It looks like a sub-$1000 Ultrabook will be real after all, though it still remains to be seen how much you will have to pay to get the configuration you desire.