Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (464.99 USD): od7off
Coupon (469.99 USD): affiliate6
(CouponsFromChina.com tip: put item in your cart and apply coupon code there after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGRM36, aff7off, bgssaff9, BGKtechredmagic
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Price history (for all/most countries) for ZTE Nubia Red Magic 3 6/128GB is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).