According to my DB the lowest price is $55.43 for 3500W 220V Mini Electric Water Heater Tankless (in Banggood). Go down and check coupons out. Remember to check price history if it is available. Let’s see what best price is ATM.
Color As pictured show, Hot Water Temperature 30-60℃, Waterproof Grade IPx4, Rated Frequency 50Hz, Rated Voltage 220V, Power Cord Length 97cm/38.18inch, Use Pressure 0Pa, Material ABS plastic+Stainless steel, Power 3500W, Plug EU
Latest price update (UTC time):
Banggood ($55.43)
Banggood warehouse is located in China. I have no active coupons for you right now. Good or bad price? Well, this price is higher than average price ($31.32)
Link: Banggood product page
Price: $55.43
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG250ccd, BG26776b, Cuponation9, BG0129d3, BG524ceb, BG735a15, BGRFANSD01, BGNINEF42, BGd2902b, BGdfbf61, BG5d9482, BGb2361c, BG69967f, BG02b07a, BG55e622, BG589b2e, BGf625a4, BG8FORMULAMX
(you can check these old coupons out, but these probably won’t work)
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Here is price history (for all/most countries) for 3500W 220V Mini Electric Water Heater Tankless.
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)).