I think places to look would depend on your location, not much point looking for one in Bali if you are in Jakarta.
Used prices : also a fluid thing- as it depends on how used.
Prices do not drop significantly from new prices until the vehicle is a whole lotta years old.
So for a one or two or even three year old scooter you are probably better off buying new, mainly because of the price and you will still have the warranty and no worries about it being stolen goods or a credit default.