Aliexpress
Click here… to search for 4000W AC 220V Variable Voltage Controller [EU] on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in Europe 
. Too bad there’s no coupon right now in Banggood. I’m not sure about the price, coz I have only 1 record(s) in my database.
Link: Banggood product page
Price: -3 USD
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Price history and price alert
There is only one database record (it was for 11.99 USD), so you can’t see price history chart.
You can set price alert (for Banggood).