Customs charged me 1000 pesos for bringing in my harmonicas

It states clearly in the list of objects you can bring that TWO MUSICAL INSTRUMENTS are allowed.

There should be an exemption for harmonicas because each is tuned to a separate key. So in a real sense, they are all one musical instrument.

You simply have to be ready with a good argument. I always traveled with my favorite B-flat or G harmonica in a leather stash bag tied to a belt loop. No muss, no fuss.