According to her, the top five most expensive Hoyas today are H. imperialis ($25-75), H. paziae ($15-20), H. bicolor ($12-25), H. buotii ($12-25), and H. siariae ($12-25) (source: BAR Digest 2007). All of them are native to the Philippines.
I quickly photographed some of the blooming ones from her collection at the Institute of Plant Breeding, UPLB. She even gave me one plant to take home, the H. diversifolia, unfortunately does not have photo here.
I would like to post this to