I bought legos and computer parts and put them together with hot glue! It runs on 60W of power.
I started with the love for legos, small computers, and design. I used LEOcad to make the intial design and bought all the bricks through bricklink.com, which is a network of lego-selling hobbyists. I kept to my design strictly, but bought used parts from my local FreeGeek when I could. It cost a little more than 300 dollars.
Everything that needs to be held in place was hot glued–really just the motherboard, button, and fan.