While I was looking for the smallest Arduino available on the market I stumbled on a website from a guy called Fabio Varesano that has developed a tiny one called Femtoduino. Not only he released the schematics, but he also gave the list of components as well as the board. Thanks Fabio!
You can check all the details on the official website: http://www.varesano.net/projects/hardware/Femtoduino
Now I know that snatching a PCB this is the hardest part since they are so small that they are not easy to build at home. So I talked to a local company and I order small batches of 10 PCBs and I can ship them to you for a total cost of 10€ each (including S/H). Ordering all the components from Mouser and assembling it yourself will cost you less than 20€ which is substantially less than the price charged by the website: http://www.femtoduino.com
So, if you are interested, drop me an e-mail (or comment below). Don’t forget that if you really appreciate this project, buy Fabio a beer ( paypal: email@example.com )