Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. Too bad there’s no coupon right now in Banggood.
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
Old coupons (from the oldest to the newest): BG6dc002b, BG589b2e
(there’s a little possibility that old coupon will work)
Price history and price alert
Here is price history (for all/most countries) for GAMTOOCA 1500W Immersion Heater.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).