Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. You can get coupon down below.
Link: Banggood product page
Coupon (7.48 USD): 2022ACTIESNL
(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): BG10OFFAFF1, BANGGOODSD, BGHealth06, 00c906
(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 Kids Electric Sonic Toothbrush.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).