An cable long enough to cross the Atlantic cost a lot. But you can also get 10Gbit dedicated line for $1000 /month with ip transit, so I don't think it's too expensive. The more bandwidth you need the cheaper it gets per Mbit. For a startup I suggest going peer-to-peer (like the bittorrent protocol) to distribute your content. Note that you can still charge for it. That's what Spotify did in the startup. With peer-to-peer it uses the user's bandwidth to distribute the content, so that you do not have to pay for the bandwidth.