Mechanics

HELLO,I GOT AN ERROR CODE P0128 AND THE MECHANIC I TOOK THE CAR TO SAID THE COOLANT THERMOSTAT VALVE WAS STUCK OPEN. HE IS ASKING 535$ FOR PART AND LABOR. IS THIS REASONABLE? I FOUND THERMOSTAT ONLINE FOR LESS THAN 20 DOLLARS...IS LABOR THAT INTENSIVE? TH

2004 Ford Focus • 92 miles