Well, a raspberry pi is a small $35 dollar Linux computer with an SD card as a hard drive and an USB cable as it's power source. While they are only $35, they perform really well!
A cluster is basically a group of computers that work together to run a very intensive program. Say for example you needed to calculate 1000 things with a single raspberry pi and every calculation takes 1 second. That would be 1000 seconds! Now if you add a second raspberry pi and you have them share the load they will be twice as fast! Imagine running 4 of them, that would cut it down to 250 seconds! Well that's exactly what I plan on doing
Below you will find a list of items you would need if you were to build a 4 pi cluster from scratch. Prices are in Euro's because that's what I pay with (I know, crazy right?)
This all adds up to ( €180.43 which is $233.76 according to google
I ordered some of the stuff from a shop in china called "banggood". Since they deliver all around the world I will add the links to those items below.