Aliexpress
Click here… to search for Xiaomi Yeelight YLYD09YL Square Night Light on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (7.01 USD): BGAFF10OFF
Coupon (7.01 USD): BGYEE20COUPON
Coupon (7.01 USD): BgcLuBofErtA10
(CouponsFromChina.com tip: paste coupon code in your cart and click Apply after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGYLYD09YL, AFfbG10, aff7off, bgchinafest, BGYEE11COU, BGLIGHT2020, BGdragonBoat, BGLIGHT0920
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi Yeelight YLYD09YL Square Night Light.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).