Depends on how many times they can re-use a core.

The upper limit comes from the fact that they are currently only reusing the first stage, and that the first stage core is ~75% of the cost of a launch.

So, if they can use a core n times, they get a % discount:

    2 38%
    3 50%
    4 56%
    5 60%
   10 68%

They are planning on additional future reuse, the next portion is probably recovering the fairings.