When I used to live in Minami-Bosou (near Tateyama), I often went to a great wine bar in Chikura called 'Liblos.' It has a great atmosphere and is only about 100 meters from the ocean. It is run by an ex-librarian named Komiya-san. I really miss the place. It is probably my favorite place in Japan to drink wine.
It is a great weekend trip from Tokyo. Highly recommended!