$59
http://handheldsci.com/kb
I can vouch it works with some Korean boards, I'm pretty sure it will work with most modern keyboards. But AFAIK doesn't work on Macbooks (the keymapping at least).
I'm working on making a knock off of these once adafruit re-stocks the BlueFruit EZ-Link, the parts for them shouldn't come to more than $30 USD realistically.
Ouch yeah 59$ is spendy and that thing looks kind of big I was thinking more of a bluetooth dongle like Dual Shock 3 controllers use with MotioninJoy, but PS3 / xbox controllers already have a little battery and probably use less power than a keyboard.
This is the
http://pcpartpicker.com/p/2N1Nn I want to make although I keep changing it as more parts are released.
Attaching the latop display to side of mATX, and putting the keyboard on something solid and flat with mouse pad just to right of 60% kb.
mATX will be able to be stood up on a custom protective bag with a solid frame so the screen will be at eye level and not crowd the area.