Price of second hand iPhone 4S?

I'm going to sell my iPhone 4S at the end of 2012 because I will need to study for medicine.
Anyway, how much should I sell it for?
I've had it from February 2012 and I've always been gentle with it. It has a screen protector and no bad scratches.
Has never been dropped, broken or submerged in water.
Australian dollar value please

About 190 Australian dollar

They go for $300us now, and when the next iphone is released in 1 month, they will go for $200 us.