In order to change the oil pump you need to drain the oil, disconnect the battery, take off crank shaft damper, and timing belt, and tensioner. The cam shaft sprocket and timing belt cover have to come off too. Then the oil pan can be removed. Assembly is in reverse order. The total cost should be about $1000 with parts. If you did it yourself you would have to buy the pump and oil pan gasket which would run you about $100.