But oil at that cost provides a huge land-rent income to the Saudis when world (market) oil prices top $50, $100, $150, $200, ... bbl.

KSA's extraction price remains $15. The rest is pure profit to them.

(Discounting the hundreds of millions of years of geological accumulation and transformation which created the resource in the first place. See "Burning Buried Sunshine" by Jeffrey S. Dukes, 2003. https://dge.carnegiescience.edu/DGE/Dukes/Dukes_ClimChange1.... (PDF).)