Aliexpress
Click here… to search for Xiaomi MIIIW Qi Wireless Charger Mouse Pad on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (28.34 USD): AFfbG10
Coupon (28.34 USD): affbg10
Coupon (28.34 USD): BGBFAFF2019
Coupon (28.34 USD): BGCITYADS2019
Coupon (29.29 USD): aff7off
(CouponsFromChina.com tip: coupon code has to be applied in shop’s 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, BG3CSUM, 502C6B
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi MIIIW Qi Wireless Charger Mouse Pad.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).