This analysis is from 2019 and it doesn't break down the cost difference for onshore vs. offshore oil. But it estimates the cost for the Saudi's at $8.98/barrel (approximately $11.01 in todays dollars).
Do you have the analysis where it says $25+/barrel. It is certainly possible that production costs have risen significantly in the last half decade.
That's why we don't take all the oil, just the offshore oil. It's significantly more difficult to conduct terrorism when you have to swim to it.