Did anyone ever state the discount SES got? To my knowledge all we got were vague notions.

In any case, considering the four-month refurbishment the reflown core may actually have ended up more expensive than a new one. That's okay for now. SpaceX offered a discount to get a customer to fly on it instead of having to pay the launch cost completely on their own. Currently I wouldn't say the discount is any indication about how much cheaper reflying a core currently is. But with the first stage being about ¾ of the launch cost there are of course great potential savings, which is where the 30 % come in.