Waterproof Rating IPX7, -30s Intelligent Reminder, -DuPot 0.15mm ultra fine bristles, -31000 Acoustic Vibration, Working Time 30 days, -Wireless Inductive Charging, Rated Voltage DC 5V, -Food Grade Brush Head, Weight 250g, Charging Time About 10 hours, Power 2W, -4 Brushing Modes.
Just check coupons out (with price alert and 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 coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. I found coupon for you. Check this out.
Link: Banggood product page
1. ($26.03): 13f142
apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): TTxBG10, aff7off, 2019SPEDM, bgssaff9, AFfbG10, BGBGHFRI15, 0e7f33, BGHOMEG12, FBCOUPON1, BGHome15%, BGHOMEA15%, BGAFF10OFF, BGCuponation10
(there’s a little possibility that old coupon will work)
Price history and price alert
Here is price history (for all/most countries) for Mr.Handx Sonic Toothbrush. The lowest price was: $19.99.
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)).