Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (283.77 USD): BGGutscheine
Coupon (286.89 USD): BG8ReviTrage
Coupon (286.89 USD): BGcoupon8off
(CouponsFromChina.com tip: you should apply the coupon in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BgcLuBofErtA10, BGAFF10OFF, BGCuponation10, 7bcdf9, BGHONEY2110, BGOxy10, BG564c1f, BANGGOODSD, ADMITAD2212, 2022ACTIESNL, Terence, Tabby20, 2203ActiesNL, BG1efeb0, 8Couponsde, MVC8SPRING, 8BGwbg2204, BG2462de, tRaDetRaCKeR, 8wEbgaInS5, pROMo8cuPoN, hoNEYbGdeAlS, BgGoodie9
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for SKYMEN 040S 10L Ultrasonic Cleaner.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).