Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. There is no active coupon in my database right now (for 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): BG79mask, BGHOMEG12, BGdigoo15, bGhOnEy10, BGOCFR571, BgcLuBofErtA10, BGELEHOME23, BGNOTD571, BGBFHOME69, BGAFF10OFF, BGHONEY2110, BGMAYSE571, BGZX571, BGTYOD571, BGRU571, BGSPHOME72, BGZXSR571, BGTYOJ571
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi Smartmi Anti-Haze KN95 Face Mask.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).