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 (20.60 USD): BG75597c
Coupon (22.06 USD): Cuponation9
Coupon (22.30 USD): BG8ReviTrage
Coupon (22.79 USD): BG00c906
(CouponsFromChina.com tip: 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
Old coupons (from the oldest to the newest): BGMA1006, BGCuponation10, 13f142, BGHONEY2110, BGAP2606, BG10OFFAFF, BGwhielabel, BG10OFFAFF1, BANGGOODSD, BGHealth06, 00c906, BGHealth10D, 2022ACTIESNL, BGHB218, 2203ActiesNL, BGHECARE1, BG4ee866
(probably won’t work, but you can try them out)
Price history and price alert
Price history (for all/most countries) for Loskii S4 Electric Toothbrush is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).