Later this month (February 2012) you should be able to buy a single board computer that runs Unix and outputs HD video (1080p) for $25. Needless to say, this is quite an accomplishment and will put low cost computers into the hands of lost of people who wish to learn and experiment. This computer is the Raspberry PI.
In the interests of full disclosure, the $25 version does not have a network connection, A version with a network connection is being offered for $35. You will also need a USB keyboard, mouse and a digital TV or monitor for a display. Assuming you already have a TV or monitor, for less than $50 you can easily get the $35 board along with a keyboard and mouse.
NPR just did an interview with Raspberry Pi’s creator, Eban Uptonon their Word of Mouth program called
You can listen to this nine minute segment by going to the link above. A primary goal of this project is to encourage young students to learn how to program by getting these computers into the hands of as many of them as possible. Their website is located at http://www.raspberrypi.org/.
Here is a video interviewwith Eban.
These boards are roughly the size of a credit card and you can see one (beta version) pictured below.