Call around to get the best price. For my car it was close to $600 for a dealer one. Cheapest price I could find, cheaper than our host. They are not all the same depending on the model and year. Some are substantially cheaper than others.
I don`t know how Tom could change it in 10 minutes, unless he is thinking of a different part. Mine took a couple of hours.
How did your mechanic come to his conclusions? Is the car running poorly?