Japan price is definitely cheaper than Singapore, if exchange rate is good. (but now Japanese Yen going too strong ~0.016)
I was tempted to get my D90 from Japan before, due to the limitation of warranty. Just forget about it.
You can find some duty-free shops in Tokyo City (eg, Akihabara area). Or you wanna refer to some of these websites.
http://www.coneco.net/list_catemaker/01105070/g2qDUoOTL05pa29u.html
http://kakaku.com/camera/camera-lens/ma_58/