The more expensive and better quality the camera the less IR is normally let through. Don't confuse looking into the IR spectrum and recording the IR spectrum. They are not done by the same sensor.
Actually IR recordings are typically done with the same image sensor as visible light recordings. What high-quality cameras do is have an IR filter in front of the image sensor that is automatically moved out of the imaging path when the camera is switched into a low-light or nightvision mode (In many cameras this results in an barely audible click when switching modes as the filter is moved).
Such cameras also typically have a collection of ND filters as well that can be switched in and out as needed for filming in very bright light to avoid having to use ridiculously high shutter speeds with a sensitive image sensor.