Just check coupons out (with price alert and history). You probably want to know what is the best price?
Built-in 3.7V 800mAh Li-ion battery, Charging time: about 15hrs, working time: about 2 – 3 weeks ,5 functions and 15 working modes,5 functional keys
Aliexpress
I could not find it on Aliexpress. Click here to search by yourself.
Here are coupons that you can use.
Latest price update (UTC time):
Price history and price alert
Price history (for all/most countries) for Smartsonic+ JK-T10 Electric Ultrasonic Toothbrush is here.
Price records source(s): Gearbest
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)).