You can create price alert here, copy coupons and view price history. You probably want to know what is the best price?
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):
Rated Voltage: 220V, Sleep Mode: 20dB, Model: MJXFJ-150-A1, Brand: Xiaomi Mijia, Applicable Area: ≤53m², Wireless Connection: IEEE802.11b/g/n 2.4GHz, Rated Frequency: 50Hz, Noise: ≤36dB, Auxiliary Heating Power: 400W, Rated Air Volume: 150m³/h, Rated Power: 20W
Banggood
Banggood warehouse is located in China. There is one great coupon!
Link: Banggood product page
1. ($514.79): BG10OFFAFF1
apply code in your basket (cart) after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): 7bcdf9, BGCuponation10, BG10OFFAFF, BGwhielabel
(these coupons are old, so probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi Mijia MJXFJ-150-A1 Wall-mounted Air Purifier.
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)).