how much should a throttle body replacement service cost in total on 2006 GMC Envoy

Firestone says that I need to have my throttle body replaced and I want to know if thier quote is a fair price

Asked by for the 2006 GMC Envoy
they can go from 300.00 to 600.00 depending on part number.what was the quote?
the quote was $470 which was $350 for the parts and a $40 gasket plus eht labor to install and do a relearn procedure. When I used AutoMD they gave me parts and labor quotes of $337.90 from a dealer or $258.83 from a shop... So I guess that I should contact my dealer and get their quote, because Firestone could only get the parts from my dealer so I am assuming that my dealer is making up for lost revenues.