It's good hear that others are working on the STM32F746.
It's also good news that ST are releasing a 400MHz '746 in late October/November time.
Back in July 2015, I also was concerned about the cost of the F7 Discovery - so I made a simple breakout board that mimics the F4 Discovery board headers, making it a plug-in peripheral compatible but running at 2.5 x the throughput.
The board is called BoB (Break out Board), is 2 layer and sized 66mm x 66mm. It has 2 x FTDI USART ports (one for flashing) , USB and a ST-Link debug connector.
The '746 is now supported by mbed, and there's a free to use 32K code size limited compiler from Keil uVision.
There appeared to be little interest in this board last year - but perhaps with a few more firmware libraries available, plus more overall experience of the F4 and F7 range, that now is a ltime to release this board.
Another possibility is to adopt the Arduino MEGA footprint - and break out the '746 GPIO to Arduino like headers.run of these professionally built in Shenzhen.
If there is sufficient interest now in obtaining a '746 board for the hobbyist - then I will consider getting a run of these professionally assembled in Shenzhen.
Whilst the pcb and connectors represent only about $1 of manufacturing cost - the price of this board will be dominated by whatever the '746 costs in Shenzhen. This can be sourced from Mouser Chinahttp://www.mouser.cn/Semiconductors/Int ... c0&FS=True
The STM32F746 is available in 100, 144, 176 and 208 pin LQFP packages - making it slightly more easier for the hobbyist market.
Prices start at around $15 for the mcu in 1 off, falling to around $8.55 in 1000off.http://www.mouser.cn/ProductDetail/STMi ... K83Q%3d%3d
Clearly this will not be comparable to a $4 STM32F103 board from fleabay - more like $25 to the end user - but hey, you get what performance you pay for.