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 (9.06 USD): 20%DG422
Coupon (10.19 USD): bGhOnEy10
(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): 50DGPO, FT12, 502C6B, a4f288, vipupgrade8, TTxBG10, BGDigoo15%, AFfbG10, aff7off
(probably won’t work, but you can try them out)
Price history and price alert
Price history (for all/most countries) for Digoo DG-LS11 Sonic Toothbrush with 2 Heads White is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).