The goal of Space X is to make the Apollo style rockets that they use reusable. Why would this reduce the price to get to space? "Musk compared it to flying today where a 747 isn’t simply thrown away after a flight to London.1" A ticket to London may not be exactly cheap right now but if the company needed to buy a new 747 for every flight the prices would be impossible for the average person.
What makes this step so important is the accuracy needed to land on such a small target. According to Space X the accuracy that they've been getting so far when recovering the first stage of the rocket was 10km. Obviously you need to be a lot more exact to land on a little platform floating around at sea. This is something that no one has ever done before, not NASA, not the military. The closest thing human's have done so far is landing the space shuttle. However, there is a huge difference between the two. The space shuttle has wings. It can control itself, once its back in the atmosphere, using basic concepts that we've understood for as long as there have been airplanes. Bringing a rocket down and controlling it with a similar level of accuracy will be an immense challenge and I look forward to watching SpaceX doing something entirely new.