As others have said, it can be done cheaply. The electricity costs more than the hardware at least for most people's setups that I've seen. (Exception is peop

As others have said, it can be done cheaply. The electricity costs more than the hardware at least for most people's setups that I've seen. (Exception is people using stuff like RPi boards from solar panels; that's almost a sub-hobby in itself.) I run mine in a basement in place of a small utility heater. If I'm going to burn the watts anyway, might as well get some processing cycles out of it.