If I am looking at the right number there are 9 Million Bitcoins in circulation at this moment, so at around 10 USD to 1 BTC that would be around 1% of all Bitcoins in circulation. Of course, if both the release and do-not-release addresses are paid $1 Mil, then that would be 2% of all Bitcoins.
It's highly unlikely you could buy up that many Bitcoins. Just attempting it would cause the exchange rate to go far above $10 per Bitcoin. Perhaps that is the extortionists plan all along though...
Either way though.. pass the popcorn, the media coverage of this will be fun to watch.
The condition was that, at the end of the transfer, the amount would be worth US$ 1M. That would actually cost a lot less than one million if done in quick successive orders as it would drive the price to the sky.