Next to the fact that NASA would rather give money to a US company, which will invest part of it to develop cheaper and more capable rockets, than to Russia, these SpaceX costs are likely to be significantly cheaper than Soyuz.

In 2007, NASA got a deal for $719 million for 5.6 tons and 15 seats. Seats on Soyuz now cost ~$60 million a piece, or $900 million just for 15 seats. The price for cargo then probably also increased.