2006 Nissan Quest • 75 miles

Wife drives 2006 Nissan Quest.I'm no mechanic.
Couple months ago -- Check Engine Light on; idling low. Dealership tells her it's a valve problem (No details which valve) -- Couple hundred bucks, its "fixed".
Now -- couple months later -- Check Engine Light on again; Idling very low again.
Dealership says it's a "Different Valve; harder to get to -- Estimated $750 just for the part". She doesn't remember which valve mechanic said it was ("Possibly Exhaust valve").

I know there's different types of valves, etc -- but seems odd one after another, in couple months -- and $750 seems steep, when checking parts on-line, and I don't see any valve parts that high -- except maybe EGR valve with gasket, at $200.
Should we trust this dealership -- I should I tell my wife she has to get a second opinion with a local mechanic --- Do you recomend a good mechanic near zip code 98021 (We are new to the area).
October 16, 2012.

What was the trouble codes retrieved for the MIL indicating?

Oct 16, 2012.