What is the simplest way to make a small low power and low price circuit that flashes LED's
Depending on how programmable/complex your flashing is - you may be able to do it without software. In which case:

Most Simple Stoplight circuit

Blink an LED with just a capacitor?

If you do need to use a microcontroller - with 6 I/O pins which is low power and small then I'd look at:

MSP430 (Value Line). Here's an app note on powering an MSP430 from a single cell (using a charge pump). There's also now an MSP430 which runs at 0.9V.

AVR PicoPower is also worth a look. Even the ATMega168/328 used in Arduino though can be put into quite low power modes.

Here's a couple of Arduino libs to do it:

http://code.google.com/p/narcoleptic/

http://www.arduino.cc/playground/Code/Enerlib