You might want to look at the glasses for video gamers and movie viewing, such as MyVu and Vuzix. You would want to harvest the lcd from the glasses. I believe you would want glasses that take composite (RCA) output, and then you could use the Video Experimenter shield to produce the composite output. It might be possible to also hack the glasses made for the latest generation of ipod, but I'm not sure of the details.
After google glasses start shipping, I would imagine we will see a whole raft of cheap clones of the google glasses made from the usual companies, and the price will come down.
As I was writing this, I ran into the US micro products site, and it looks like there is a 0.5" lcd that might fit your bill: http://www.usmicroproducts.com/displays/pmoled/usmp-p24701
. I don't know if you can order quantity 1 from them, but it may be useful to ask. Given it is 72x32 pixels, you might be able to display 4 lines of 12 characters.
Thanks for your answer. Good ideas, but will need some work to make those displays transparent.
I started thinking about using a half silvered mirror to reflect a back-lit LCD to the eye instead of putting it in the optical path. the problem with that method is that the distance from the ocular to the focal plane is tiny and I'll have to put additional optics because the LCD couldn't be placed right in the focal plane.
The display you linked to isn't transparent and too large to fit in the optical path, maybe if I'll use a half silvered mirror I could use that type of display. thank again.
I know there is an of-the-shelf solution (that can be controlled with an iPhone) I just cant find it...