Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. Too bad there’s no coupon right now 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): BGHLARO, BGHLAHUM, BGHOMEAPP, BGTT10, bGhOnEy10, BGHLHUM4L, 7bcdf9, BGSS10%SW, bgshOOp10, BGHome15%, BGHOMEAPP13, BGHOMEA13, BGCuponation10, BG10OFFAFF, BGwhielabel, BG10OFFAFF1, 6GSGIT, 00c906
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Do you need price history chart (for all/most countries) for Xiaomi Happy Life 4L Humidifier? There we go.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).