By far, the largest cost in a rocket launch is the cost of the rocket itself. By making the first stage of the rocket reusable, Space X can drop the price of a rocket launch from the traditional $100-$250 million all the way down to $55 million. That number will likely drop even further as reusability improves over time.

Ultimately, reusability will bring the cost low enough to make the Mars Colonial Transporter (another Space X project) a reality.

The video below was shot with a hexacopter. One of the keys to reusability is having the booster separation occur early enough in the launch so the rocket is still moving relatively slowly. Amazing to watch.