Battery Capacity 2000mAh, Waterproof IPX5(Not Inverted), Operating Temperature 0-70℃, Material ABS+PP+Electronic Component, Power Supply Type-C Charging Cable, Working Life ≥50000 Times, Installation Method Seamless Wall-mounted, Color Black/White, Operating Voltage 3.7V, Working Current 200-400mA, Maximum Capacity 300ML, Infrared Distance 3-6cm.
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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.
Link: Banggood product page
1. ($19.99): BGcd7a51
2. ($27.25): BG589b2e
put item in your cart and apply coupon code there 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): BGXPJA66, BGAlerabat1, Terence, Tabby20, 2203ActiesNL, BGd9a71f, BG1efeb0, 8Couponsde, MVC8SPRING, 8BGwbg2204, tRaDetRaCKeR, 8wEbgaInS5, BGHU2108, pROMo8cuPoN, BG00c906, BGJUNXW1, BGHU2365, Cuponation9
(these coupons are old, so probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for Xiaowei W1 300mL Wall Automatic Soap Dispenser. The lowest price was: $18.99.
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)).