Just check coupons out (with price alert and history). Let’s see what best price is ATM.
Product size: 190x190x324mm, Humidification capacity: 4L, Net weight: 1.65kg, Wireless connection: Wi-Fi IEEE 802.1 1b/g/n 2.4GHz, Model: MJJSQ04DY, Working noise: ≤38dB, Rated voltage/frequency: 220V-50HZ, Rated power: 25W, Tank capacity: 300mL/h
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest price update (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: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGRMJ4L300, bGhOnEy10, BGHome15%, BGHOMEAPP13, BGHOMEA13, 7d18f7, BGCZXMGREW, BGMJJSQ04DY, BGQ04DYCZ, 13f142, BGJSQ04DYCZ, BGCuponation10, BGRTQ04DYCZ, BG04DYCZ, BG10OFFAFF, BGwhielabel, BG228899, 7bcdf9, BG10OFFAFF1, 6GSGIT
(probably won’t work, but you can try them out)
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – Xiaomi Mijia 4L Smart Humidifier MJJSQ04DY [EU] ($-3)
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi Mijia 4L Smart Humidifier MJJSQ04DY.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).