Aliexpress
Click here… to search for Xiaomi Deerma Clothes Hair Ball Remover on Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (18.27 USD): BG2020NS
Coupon (19.34 USD): AFfbG10
Coupon (19.99 USD): aff7off
(CouponsFromChina.com tip: you should apply the coupon in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Old coupons (from the oldest to the newest): TTxBG10, bgssaff9, TS15prime, TISPrime01, Tools1, Tools3
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Price history (for all/most countries) for Xiaomi Deerma Clothes Hair Ball Remover is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).