Raspberry Pi 2 vs STM32f429I Discovery?
RPi is a full-featured, ready-to-use product. It is mass-produced and used widely mostly by individuals. Contrary, Discovery boards , as many of other evaluation boards are development tools used, as named, for evaluation of a specific technology in order to make another product, potentially with much lower cost. Being a tool, it is produced in much lower volumes and targeting mostly companies rather than individuals. So the volume and the target consumers are the factors setting the price.