But i am interested in MCU which can build system with minimum or no external hardware.
That depends on what "external hardware" you need, the cheapest will not be a chip with an A/D converter if you do not need an A/D converter. Have a look at the Philips LPC7xx chips and post again (they all sell for less than $1.50 in your small quantity). If OTP is problem you will need to use the LPC9xx chips with flash (samples available, production quantities soon), they are basically the same as the LPC7xx save the fact that they are two clockers and abt a buck more.

Erik