The ChipWhisperer-Nano is the lowest cost platform for performing side-channel power analysis attacks in training and educational environments. This device has a smaller subset of features compared to the ChipWhis-perer-Lite or -Pro, but still allows you to perform many of the tutorials and demos.
The use of synchronous sampling ensures that this low-cost device can be used for performing real power analysis of algorithms and devices. The built-in target is a STM32F303F4P6, which has 16kB of FLASH and 4kB of SRAM.
The ChipWhisperer-Nano has a built in bootloader for its target board, meaning no external equipment is required!
Available from Mouser
Also available in a pack of 20 from Mouser
Also links to documentation