Currently the 299EUR Asus Eee PC is one of the cheapest notebooks you can get but once the Silverthorne platform is on the market manufacturers will be able to create small notebooks for as low as 150EUR.
The Intel Atom processor has 47 million transistors, runs at a frequency of 1.8GHz and uses only 0.6W to 2.5W. The performance of Atom will be close to the performance of the first Pentium M "Banias" processor.