Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. Only one coupon available!
Link: Banggood product page
Coupon (8.26 USD): BG00c906
(CouponsFromChina.com tip: paste coupon code in your cart and click Apply 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): BG97a93f, BG75597c, BG3a45f4, BGbc238a, BG15fd01, BG58c4fd
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for 5 Modes Sonic Electric Toothbrush with 4 Heads.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).