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 (51.29 USD): bGhOnEy10
Coupon (51.29 USD): BGdragonBoat
Coupon (51.29 USD): BGAFF10OFF
Coupon (51.29 USD): BgcLuBofErtA10
(CouponsFromChina.com tip: you should apply the coupon in your cart 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): e2bcea, TTxBG10, 2019SPEDM, BGss506, bgssaff9, AFfbG10, 502C6B, BGBFAFF2019, BGCITYADS2019, BGMPB2020, BGSS10%SW, bgshOOp10, BgoFErTaSchInA10
(probably won’t work, but you can try them out)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi WiFi HomePlug.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).