There are very good TI Cortex M3 and M4 Tiva Launchpad boards (for $12.99) and for the ultra low power applications the MSP432 cortex M4 launchpad boards (for $

There are very good TI Cortex M3 and M4 Tiva Launchpad boards (for $12.99) and for the ultra low power applications the MSP432 cortex M4 launchpad boards (for $12.99) with very good documentation and support.