Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in Hong Kong. CouponsFromChina software could not find any coupon for this product in Banggood.
Link: Banggood product page
Price: -3 USD
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGOP9P256, BGOP9P25, 13f142, BG9P8256, BGOP9P8510, BGOP98IT, BGOP9P8D, BGOP9PT, BGOP9P8J, BGOP9P86, BGOP9P8IT, BGOP9P2561, BGOP9P72Z, BGOP9PIS, BG6f86d5, BGb4dc73, BGb39824, BG20097a, BGOP9P256725, BG332b2c, BG7a8ec7, BGa23e52, BGffbb63, BG435175, BG307986, BG9eff28, BGfe5ee4, BGa2b2b9, BG33040d, BGdbaab8, BGcc70ae, BGfe85b3, BG963909, BG7f3476, BG6d360a, BGf582f9, BG1685fc, BG9504b9, BGcf3bd6, BGfbab8f, BG92a5e8, BGee475b
(probably won’t work, but you can try them out)
Price history and price alert
Price history (for all/most countries) for OnePlus 9 Pro 5G 8/256GB Snap888 Global ROM is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).