- STM32F407VGT6 (MCU): $9.29 (directly from STM, with 1000 pcs quantity),
- LIS302DL (accelerometer): $6.8 (Farnell, no price info on STM pages),
- MP45DT02 (MEMS microphone): $2.87 (Farnell, 500+ quantity),
- CS43L22 (DAC): $3.12 (Mouser, 100 pcs),
- STM32F103C8T6 (another MCU working as USB to SWD bridge, on-board ST-LINK/V2 debugger interface): $3.1 (STM, 1000 pcs),
- ... and PCB and bunch of discrete parts.
It definitely looks that STM is not making money with this board but sells it as a promotional product to popularize STM32F4 series microcontrollers. If you are interested in this family in particular or if you need relatively high-performance platform for audio processing this would be great buy. On the other hand this is kind of "bait and switch" offer as STM32F407VGT6 in small quantities has similar price to the whole development board. Other drawback (comparing to older STM32F103 board) is that ST-LINK part can not be detached by splitting PCB into two pieces.