Mode memory function to record your preferences and habits, a good companion for travel, 31000 times per minute high-frequency vibration, Rust-free and metal-free brush head, strong teeth cleaning, safer and healthier, 25 days of endurance, Rated voltage: 5V, Charging time: 4 hours, Battery capacity: 700mAh, Rated power: 2W.
You can create price alert here, copy coupons and view price history. Let’s see what best price is ATM.
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. I’m afraid that there’s no working coupon in Banggood.
Link: Banggood product page
Price: $-3
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!
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): BGST300, AFfbG10, BGT30022, 502C6B, BGBGHFRI15, 0e7f33, BGHOMEG12, FBCOUPON1, BGCNT300JP, BGCNT300July, BGSJHome38, BGSepPro27, BGHome15%, BGHOMEA15%, BGTOOBEUR, BGBTJU51, BGBTJU29, BGAFF10OFF, BGCuponation10, BGXIAOMICN, 13f142, BG10OFFAFF, BGwhielabel, BGXPDC21, BGGRE094, BG10OFFAFF1, BANGGOODSD, BGHealth06, BG589b2e
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Price history (for all/most countries) for Xiaomi Mijia T300 Sonic Toothbrush is here. The lowest price was: $18.99.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).