I just bought a STMicroelectronics NUCLEO-F746ZG for $23.
This is an amazing board. Here are some key features.
STM32F746ZGT6 in LQFP144 package ARM®32-bit Cortex®-M7 + FPU + Chrom-ART™ Accelerator 216 MHz max CPU frequency 1 MB Flash 320 KB SRAM 12-bit ADCs with 24 channels (3) 12-bit DAC channels (2) USART/UART (8 ) I2C (4) SPI (6) Advanced-control Timer (2) Low-power Timer (1) General Purpose Timers (12) Watchdog Timers (2) CAN 2.0B active (2) SAI (2) USB 2.0 OTG HS USB 2.0 OTG FS Ethernet 10/100Mbps Virtual Com port Mass storage (USB Disk drive) for drag'n'drop programming Debug port
All CPU pins of the LQFP144 are available on the board.
I ran benchmarks with the ChibiOS/RT RTOS at 216 MHz CPU speed.
This Cortex-M7 board can do 4,909,064 context switches per second. That's about 0.2 µs for a context switch!
This is 3.5 times faster than a 100 MHz Cortex-M4 NUCLEO-F411RE.
I am using ChibiStudio for development. It's a great Eclipse based IDE.