The cost of small microcomputer boards is so low that I can add a node per day to a supercomputer cluster just with the lunch/snack/drink money I save while on my diet. While perhaps not the fastest, the latest $9 C.H.I.P. board is small and draws little power. Pictured here is a six node cluster of Raspberry Pi. While their price tag reads $40 each, they have 4x the cores plus a graphics processor chip. General purpose graphics processing units are often at the heart of serious compute intensive clusters. Then there is the $99 Parallallela with a slower 2 core main processor but a massive 16 core co-processor chip.
Building a small supercomputer is a great project for a science fair, Maker Faire, or just for fun. Interested? Stop by the MakerSpace or contact us online.
PS. I am the former systems manager of the Northeast Parallel Architecture Center, a NSF funded supercomputer site hosted at Syracuse University.