How much should it cost to replace an O2 sensor?

Your Lexus has 3-4 Oxygen Sensors at least. The front ones are a special type called Air Fuel Sensors and can be pricey. The front ones run about $411 each and the rear one runs about $217 parts and labor. So make sure that you know which one to replace. here are some shops: https://repairpal.com/lexus-repair-in-slidell-louisiana