it will depend on the island itself. If you go the nearest one it will be very busy and too crowded. I will suggest you to go a little far away from the mainland, such as Ayer and Pelangi or even Tiger island (Pulau Macan).
Here is the Ms. Nyai, mobile no. (62) 8128921517 the travel agent who use to take our family and my friends trip to thousand island. you can contact her to get so many range of options where to go and how much it will cost you.
hope this will help.