STM32 ARM Cortex M3 boards (STM32F103) are available starting from $1.85. Not sure why the price gap wilth SAMD21 ARM Cortex M0(+) boards is still so large. 
STM32 ARM Cortex M3 boards (STM32F103) are available starting from $1.85. Not sure why the price gap wilth SAMD21 ARM Cortex M0(+) boards is still so large.