Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in Hong Kong. There are no active coupons for this product, but the price is pretty low isn’t it?
Link: Banggood product page
Price: -3 USD
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGOCLE148, 2019SPEDM, BGOcleanX, BGalibuy8C, vipupgrade8, BGMIB2, AFfbG10, BGBGBG2, aff7off, BG2GWTR, BGC42083, BGT00thXX, BG0CleanX, BGDCHU29, 903776, BGTooth2, BGHU42083, BGigX2, BG2Oral, BGBFAFF2019, BGCITYADS2019, BG00C2, BGKKK2, BGMumlatzimX, BGT2Br2, BGVDay10%off, BGAFF10OFF, BGTT10, bGhOnEy10, BGbeauty001, BG2OCX, BG42083, bgshOOp10, BgoFErTaSchInA10, BgcLuBofErtA10, BGC2083, BGOCX449, BGCuponation10, BGOCX8, BG22371, BG10OFFAFF, BGXPAP246, BGHB218, BGHUAP252, tRaDetRaCKeR, BGHECARE1, BG9660e3, BGc49bc6, BG4ee866, BGBWITHUSIN5, BGBWITHUSJ75
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Price history (for all/most countries) for Xiaomi Oclean X Sonic Toothbrush White is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).