Yes i agree Google-X plans are ambitious.It's really hard to tell how unrealistic are they, but they did achieve some pretty brilliant results(self driving car driving 700K miles, Google loon progress[1]), And as for price, Google do seem to be mindful of prices. As examples: their self driving car, used as a taxi would be very affordable,Google loon is aimed at the 3rd world(so they surely planed for costs),Their glucose lens don't seem expensive(electronics are usually cheap) - but surely sell for a good price.
[1]http://www.quora.com/How-is-Project-Loon-doing