Most analyst consensus is Saudi is operating at a loss, compared to their spending, not the cost of producing oil.
But they also started into this price drop with nearly $800 billion in cash reserves. I don't think Russia or the other OPEC nations are near that point, relative to their spending.
Saudi oil production is actual down from last year at this time.
When you have $15-20 billion/month in subsidizing commitments, internal and very proximal security problems and you remain a profligate consumer of imported goods, cash reserves dwindle quickly.
End of story.