The margins for Ultrabooks are lower than for regular notebooks. So they're not only higher in cost but also make them, the manufacturers, less money per unit sold, and as you saw in this very thread they're not selling that many either.
Theses high costs come from a few critical parts manufacturers
who have enough control over the market to substancialy raise
their prices, as is the case cuurently with hard disks ; CPUs being
first on this list , remeber the intel s 250$ minimum price point
for regular its 17W chips.
No wonder that with such high margins it s not possible to reduce
the price of the complete thing to about double the CPU (high) cost...
The OEMS actually pay more for the parts because of the required mSATA SSDs or SATA SSDs, usually magnesium or aluminum chassis (which is quite expensive) and non-standardized batteries that they order in lower volume (remember that you can't swap an ultrabook battery with a regular laptop battery and since they order many more swappable laptop batteries the cost is lower due to volume).
Ultrabooks are more expensive because the parts are more expensive.
For who is in the know about industrial prices , things as aluminium
or magnesium are negligible quantity , while the rest , plastics all over
the place is worth one $ per kilo , including forming costs....
As for batteries, their cost is in direct proportion of their capacity ,
the so called slim form factor being irrelevant in matter of added cost.