I would get a bunch of Raspberry Pi's, overclock each to 1GHz and create a supercomputer!!!

4x RPi = 4GHz = £100 (Approx $160)
10x RPi = 10GHz = £250 (Approx $400)
100x RPi = 100GHz = £2500 (Approx $4000)

Don't know if it works though!!!

Later,
Roxie - Girl With Blade