Yes, the body is made of brass, but the fingering system, the reed to vibrate to make sound, mouthpiece configuration & so forth are all woodwind characteristics; it is classified as a woodwind. (The saxophone inventor created it to make a bridge between woodwinds & brass in the orchestra.) Brass instruments do not have a reed, just a mouthpiece to buzz on to make the sound. That’s the difference.
I don’t think Mittens is talking about the expense of the card & wrappings & such, but rather that the box & paper are the really cool things, according to the cat.
The translation/lyrics of the song have nothing to do with the joke. The gag is that everyone in the family is singing along until Baldo comes in & does NOT join in. The gag, such as it is, is that he is not a singer/his interests are not in lyrics/singing but in mechanical things. The song could be in English, German, Chinese; it wouldn’t matter to the joke. You don’t need to know Spanish to get that.
The joke isn’t about the cost but the fact that the hotel is right across the street & he is taking a taxi. They are charging him an awful lot to go across the street, however.
It’s not even a human’s song