Price to replace Prius Coolant Control Valve

Yesterday. I took our 2009 PRIUS to the Toyota dealer to have the 90,000 mile service performed and have the check engine light reset.  The service was okay but the service engine light issue baffled me.  The computer code for the check engine light recommended that the dealer replacement of the  Coolant Control Valve was necessary.  Toyota service bulletin EG001-08 M.I.L. “ON” DTC P1121 cited that this valve was prone to sticking and that the time to replace was 2.1 hours.  Looking at the service bulletin process for the valve replacement, the time seemed reasonable.  So my comment or "speaking out" is this.  Why would the dealer want to charge me $505.00 to do this?  I guess it must be to never want to take my car for servicing there again and find another location at half the price to do it!!