netflix is not live shows and netflix screwed up their distribution of data in the last year which is why they are having all these problems and HBO Go and others come in crystal clear
most video is not streamed over the internet, but is on a CDN inside the ISP's network or there is a direct peer connection between the video provider and the ISP
figure $2 per month per megabit that you will have to pay to get MLB to deliver you the data. so for a 5 megabit somewhat HD feed the service will cost $60 - $70 for the season out of the current $150 price. add in the rights to the games and you're looking at close to $300 for the season to stream your local team
Live doesn't matter that much; whatever the content, it still has to be streamed on demand. Like Netflix, MLB can make direct connection deals to give them more bandwidth under high demand. Might involve short delays, but I don't see that as the deal breaker. But you are right, it would be expensive, even if it could be done within the current tangle of broadcast rights (which I doubt).