This light is available from UK distributors for about £40, which works out to about US$80. Some of the online shops will ship to the USA for another $20 or so, with shipping from these online retailers also available elsewhere worldwide.
For product and buying information, visit Bicygnals. I know Sue (who published a bike haiku today has been looking for something like this. These run over $100 including shipping, so I think I'll stick with hand signals for now.