You can create price alert here, copy coupons and view price history. 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):
Charging Way Type-C, Waterproof IPX7, Color White, Noise Level <68 dB, Water Pressure 5-120PSI, Net Weight 239g, Voltage DC3.7V, Battery Capacity 1500mAh, Product Size 63*77*222mm, Charging Indicator Slow Flashing, Material ABS, Water Tank Capacity 180ml
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($38.24): BGHB218
2. ($41.84): 2022ACTIESNL
3. ($42.29): BG00c906
coupon code has to be applied in shop’s 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): BGXPJA131, BGXPJA10, BGHealth10D
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for Electric Cordless Water Flosser Oral Irrigator 5-120PSI 180ml.
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)).