Honda Throttle Position Sensor?

I own a 2000 honda civic dx. The engine light came on and I went to an auto part store near the highway that said the code was Po122 -- throttle position sensor error. I was told the part costs 46 dollars. Took it to a mechanic who charged 97 dollars for "pinpoint" inspection and told me the entire housing would have to be replaced and not just the 46 dollar part -- total cost 750 with labor. Is he telling the truth or is there a cheaper soluition?