As per this media release dated April 28, 2016.

"Delta orders 75 firm CS100 aircraft with options for 50 more CS100 aircraft...Based on the list price of the CS100 aircraft, the firm order is valued at approximately $5.6 billion US. "

This makes the plane $75 million per unit.

http://www.bombardier.com/en/media/newsList/details.delta-air-lines-and-bombardier-sign-largest-c-series-order-for-u0.bombardiercom.html