Dan Rayburn at the BusinessofVideo has put together an interesting analysis of what it costs Netflix to deliver a streaming movie.
Based on the three cents per GB assumption, that means it would cost Netflix about $0.06 to deliver one SD movie and $0.09 to deliver one HD movie. Those numbers would be about 25% lower if the length of the movie were ninety minutes instead of two hours. It would also be a little lower or higher depending on the exact bitrate since some movies are streamed higher and some lower and Netflix only has about 400 movies available in HD. Taking all that into consideration the average cost to Netflix to stream to the XBOX 360 is about five cents per movie. Streaming to the PC is a lot cheaper, about half that cost, as the bitrates are much lower.
Based on those numbers, their streaming offering looks like it would save them tons of money and make them a lot more profitable since Netflix spends about 78 cents out and back for standard pre-sort first class mailing of their DVDs. But the one problem is that these streaming costs do not yet include the licensing costs from the content owners. It's the costs associated with licensing the content that really makes or breaks their streaming service, not the cost of bandwidth.