Display Size 6.39 Inch AMOLED, ROM 512GB, AIE 4th Generation AI Engine, 4.45V High-voltage lithium ion polymer battery, RAM 12GB, GPU Adreno 640, Resolution 2340*1080 Pixel, Battery(Built-in) 4000mAh(typ), 3900mAh(min), 7nm, OS MIUI 11, CPU Snapdragon 855 Plus Octa Core (max to 2.96GHz), (1×2.96GHz + 3×2.42GHz + 4×1.80GHz).
Check coupons or create price alert down below. Best price?
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($743.99): od7off
2. ($790.99): 7bcdf9
apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): BGM9P10, BGBFAFF2019, BGCITYADS2019
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Price history (for all/most countries) for Xiaomi Mi9 Pro 5G 12/512GB Black is here. The lowest price was: $719.99.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).