Wisnu:There many gyms in Jakarta Timur as well as other part of Jakarta, depend where the area you'll be staying there. Most of new real estate has nice gym, some of them exclusive for member but you can always negotiate. Rafles hill and Kota Wisata Sport Club (I was living here till Aug 2005) are among the best. Some open to public for Rp. 50,000 - 100,000 (US$ 6 - 11)per entry. Most of new mall also has gym open to public.
You may also consider visit the National Sport Center Senayan - South Jakarta - where the national athletess are there.
Many thanks!