Originally the average cost was estimated at $241M per tanker ($43.16B for 179 tankers). This latest order costs $153M/tanker - a massive saving of 37%..... and this order includes " spares, support equipment, spare engines and refueling pod kits."
Looking at it from afar, it seems like a big financial inducement to get an order for 18 more tankers and keep the production line going.