Nissan Repair: egr valve, intake ports, nissan dealership

Question
I have 2000 Maxima SE with roughly 150,000 miles, the code came up for the egr valve so we had that replaced, the code is still coming up.  The dealership is now talking about removing the top of the engine to clean some ports and says it will take about six hours and $500.00 does this sound correct?  I have not had great results from this dealership in the past and am leary of anything they say.  I am also being told that nissan codes are hard to interpret for anyone except a nissan dealership.  

Answer
Mark,

Yes, the answer is cleaning the intake ports where the EGR flows.  Yes, it is expensive so I know how you feel.  But, it has to be done.  You could do it yourself and save some money.  But, this is one of those jobs I do not like to do either.  Cheap at twive the price since it is so labor intensive.