Full frame cameras are below $1000. The sensor is probably quarter of that. But your camera module for Raspberry Pi will cost more than $1000. You save some by

Full frame cameras are below $1000. The sensor is probably quarter of that. But your camera module for Raspberry Pi will cost more than $1000. You save some by getting rid of the camera display and buttons. But you still have to design the camera control board, the lens mount or lens, and the housing. You are doing it on small scale, while the camera makers on doing it at large scale and with lots of expertise. This is why everyone who wants better sensor buys a camera and attaches it to Raspberry Pi. I am surprised that there isn't a 1" camera module, that is natural place for better sensor but still fits on board and could use C-mount lenses.