From my first source :
If you want to go to Giliyang Island, you can go there by ship for one time, (I mean just for go or go back). The price is only Rp 8.000,00 for one person from Dungkek harbor. Thats need 45 minutes. But, you can also rent ship for your round trip (your full travel) and the price is Rp 175.000,00. All visitors who have been arrived in Giliyang Island can use the services of a motorcycle to travel around the island. The charge around Rp 30,000 for one person. 30 minutes is enough for around the island.

http://www.pulaumadura.com/2015/12/mengunjungi-wisata-spot-oksigen-pulau-giliyang-sumenep-madura.html

From my second source : 
If you want to go to Giliyang Island, you can go to Dungkek Harbor by MPU (Mobil Penumpang Umum). The price is Rp. 15.000,00 for one person. But if you want to use your own car or other transportation, you can board out your own to people in Dungkek. Trust, your own transportation will be safety. Than, from Dungkek you need Rp. 10.000,00 for yourself to go to Giliyang by regular ship. The ship will start at 10 am so you must go there before that time. You can also use a ship services for your full trip to Giliyang and need Rp. 400.000,00 for that with the maximum capacity of the ship is for 30 people.

Sources :
http://mediamadura.com/inilah-tarif-untuk-wisata-ke-giliyang/
http://portalmadura.com/inilah-tips-berkunjung-ke-pulau-giliyang-19811