Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (27.36 USD): BG75597c
Coupon (29.29 USD): Cuponation9
Coupon (29.61 USD): BG8ReviTrage
Coupon (30.26 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): BGMAY09, BGwhielabel, BGHU0509, BGjune13, BGxmts100, 13f142, BG10OFFAFF1, BGHealth06, 00c906, BGHealth10D, 2022ACTIESNL, BGXPFE211, BGHB218, 2203ActiesNL, BGHECARE1, BG4ee866, 9OFFSUMMER, BG7ce7b3
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Here is price history (for all/most countries) for 2x Xiaomi Mijia T100 Sonic Toothbrush with 2 Heads.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).