Price history, coupons and price alert are available on this page. 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 coupon code price check (UTC time):
, Temperature 0 ° C ~ 50 ° C, Battery pack Lithium 2000mAh / 3.7V, CO2 400 ~ 99999ppm, Humidity 0 ~ 99%, Wireless connection WiFi 2.4 GHz, Bluetooth 5.0, PM2.5 / PM10 0 ~ 500ug / M and sup3, Weight 143g, Area 63.6 * 46 * 54.6 mm, 1A, Product Air Quality Monitor, 59.9 * 49.9 mm, Screen Grease in one color, Brand ClearGrass (Xiaomi Cooperation Brand), Energy input 5V
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($67.99): BGTYOJ758
2. ($78.99): BGTYOT758
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): BGXINPI758, BgcLuBofErtA10, BGDEFR758, BGDETD758, BGAFF10OFF, BGCuponation10, BGMATH758, BGMAFO758, 13f142, BGHONEY2110, BGMAYTD758, BGQP758, BGISF758, BGTYOC758, BGISOD758, BGTYOD758, BGTYGQ758, BANGGOODSD
(these coupons are old, so probably won’t work)
Price history and price alert
Do you need price history chart (for all/most countries) for ClearGrass Air Quality Monitor? There we go.
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)).