For me, personally it would be in the ballpark of 50%. I just don't see this regime as being very trustworthy or serious about rolling back the trend of nationalization in the oil sector that has been the dominant feature of this ruling family.
I tend to kind of agree that a very high discount rate is appropriate, but, I do not see how Saudis will agree to even discussing 30% let alone 50% discount rate. They will rather quietly go to Institutional Investors Pre-IPO and allow them a major buy in share. There is no doubt that Saudis are unreliable and too many risks at play.