Furthermore the Gemara Menachos 44a writes that it rises from the sea every 70 years and therefore it is expensive. Rashi there explains that it is valuable because of its rarity and unavailability the other 69 years. This does not correspond with your un-sourced assertion that during the Beis HaMikdash when it did come every 70 years it was plentiful. I would like to hear a source for your assertion; I searched the DBS Torah Library and did not find it in any Medrash or other sefer.
