I finally got around to looking under the hood of my C230...
Air Mass Meter is, indeed, a simple replacement - one hose clamp, two quick cam type fasteners, and one eletrical connnection.
I'll likely drive it a while longer and see if the Check Engine light comes back on. If so, I will then have Auto Zone check the codes. If consistent with the dealer's diagonsis, then I'll order the part from the web. Appears $300-320 is typical for part on-line.

Trunk Release Switch - I also followed guidance from this forum and removed the shift console wood panel (gently pry up plastic frame around shifter, then carefully pull up on the wood panel, lift panel up and over the shifter and disconnect the two electrical connectors). But, to may dismay, I discovered the trunk release switch is an integral part of the switch panel that is attached to the back of the wood panel. It cannot be seperately replaced. So, it appears the dealer was correct when they told me the replacement switch their parts dept. ordered for me would not work. I have glued the broken switch cover back onto the switch panel (snapped near the rear pivot point), but I don't expect it will hold past one or two uses.