Saudis budget for 2015 is $65bn and will therefore need to draw on reserves of approx. $100bn to maintain all their social programs and subsidised programs which I believe gives the Saudi's 5 years of doing this until they run out of reserves.
clearly they will not but also it indicates they have the capacity to run at low prices for a good period of time, which means whatever objective thye have in mind it appears they have the capability to implement it - be it kill USA prod, Russian influence in Syria etc etc.
