Google "OEM honda parts" for online dealers. They're usually 20-40% cheaper than the local dealer. Just input your model or VIN and it'll show the parts for car.
P0401 is EGR insufficient flow. Meaning the EGR valve and/or the EGR passage is clogged with carbon.
This is usually pretty easy to fix. Remove the EGR and clean it with carb cleaner until the plunger moves freely when you push it with your finger. Replace the gasket if necessary. Then reset the ECM/PCM by pulling the ECM/PCM fuse in the under-hood fusebox for at least 10 seconds (this needs to be done with the ignition OFF). If the code comes back, remove the airbox and clean the EGR passage with carb cleaner. It's a little hole at the edge of the throttle plate on the sidewall of the throttlebody.
EGR looks like this:
BTW: I'd fire your mechanic.