Aliexpress
Click here… to search for Xiaomi Smartmi Electric Heater on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Price history and price alert
Here is price history (for all/most countries) for Xiaomi Smartmi Electric Heater.
Price records source(s): Gearbest
Click on image to enlarge. 
You can set price alert (for Banggood).