Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (233.99 USD): BGCITYADS2019
Coupon (241.79 USD): od7off
(CouponsFromChina.com tip: apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Price history and price alert
Price history (for all/most countries) for OPPO Realme X 4/64GB CN Blue is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).