Basically copy coupon, view price history or create e-mail price alert. What is best price?
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest coupon code price check (UTC time):
Input Voltage: DC 5V, Working Time: 180 Days, Model: P4, Battery Capacity: 2500mAh, Size: 247*26*26mm, Vibration Frequency: 32000 – 38000reps/min, Charging: Type-C 5H, Net Weight: 123g, Waterproof: IPX7, Brand: Usmile, Noise Standard: 63dB, Handle Material: ABS Resin
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($73.59): BGCAPITALOS8
2. ($73.59): BGCOUPERT8
this code has to be applied in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG83d8eb, BG4ee866, BG3c2be2, BGUSEU03, BGHOM036, BG8ReviTrage, BG9c1e0a, Cuponation9, BGc8fc9d, BG75597c, BG4a7fd1, BG589b2e, JanBGCoupon8, BGSaleFeb8, BGSaleAD, BGMARCHSALE, BGAUGUST8
(probably won’t work, but you can try them out)
Price history and price alert
Do you need price history chart (for all/most countries) for Usmile P4 Sonic Toothbrush? There we go.
Price records source(s): 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)).