The bandwidth used when live streaming a camera is anywhere between 65KBps and 150KBps. Please note that this bandwidth is only taken when a camera is being actively streamed. Otherwise, the upload bandwidth consumption is around 0.25KBps during normal operation.
Also, if the camera is being streamed locally, no WAN bandwidth is consumed as all streaming occurs over the LAN.
You can view the bandwidth usage of any camera navigating to a particular camera. At the bottom of the page where the video player is, you'll see bandwidth graphs for that camera.