Ah yes, the Prioritas.
But with the introduction of the S8 now, the prices of the S7 will drop rapidly. In no time you will get one cheaper. I skipped the iPhone 6 on purpose, rather happy with the 7 though.
There is also a Facebook group called "Buy and Sell Jakarta" btw; it is mainly used by expats (moving out). There I saw some iPhones for sale rather recently.