How much should it cost to replace a thermostat in a cadillac?

My boyfriend has a 2003 Cadillac CTS. His engine light came on and the dealer told him it was his thermostat. They then told him it would cost 544 dollars to replace it. I think its ridiculous! Is that insanely high or do they really cost that much? I know a dealer will always be high but he used to work there and he thought it was under the extended warranty.|||All I can say is WOW, just WOW. $544! UNBELIEVABLE. A thermostat is about a $20 part. Replacement shouldn't take more than half an hour. Any shop will charge a one hour minimum for the work. Most cars can get away without even draining the radiator, just a top-up at the end.|||that isnt right, my wife drives a 2004 cts and i dont remember exactly what we paid, but i did it myself its real easy, ans was under 30 dollars i know for sure, im thinking it was right around 20|||i think is too high but i never worked on a car like that call other places and look around before you do anytrhing back to your question yes i think is to much