"The Falcon 9 experiences major temperature changes during its flights, as well as intense pressures and vibrations from the winds in the atmosphere. These all produce wear-and-tear on the vehicle's hardware — meaning the rocket might need repairs and updates before it can launch again." This kind of refurbishing is why the Space Shuttle ended up being way more expensive than expected. Fortunately, the Falcon 9 is not nearly as complex.
This is now the true test of SpaceX's design talents; if the rocket is built to be durable, then repairs and replacements could keep relaunch costs very low indeed. Steve Poulus, a former NASA project manager, suspects final costs could be driven below a million dollars. That figure would give SpaceX the capability of easily underbidding any competitor for government contracts, not to mention bringing it into affordability for any number of companies who'd like to put a satellite in orbit.