A cheap board already exists, the only difference is that it uses a PIC. But I believe that a Arduino kit is interesting too, many people request Atmega328 because they can mod it. But I believe that there is a better solution.There are kits that uses an STM32F103 that has alread an Arduino core (see http://stm32duino.com there are 3 cores!) for example the DSO138 cheap cheap oscilloscope. The MCU is also cheap and has 5volt tolerant pin but it is a Cortex-M3.I believe that people that ask for an Atmega328 can use an STM32F103 too. STM32F103 is faster, has more pins, more flash, more ram and has DMA.