When I was updating this page the price was 19.99 USD for WIFI Digital Wattmeter EU Plug 220V (in Banggood). Basically copy coupon, view price history or create e-mail price alert. Best price?
Latest coupon and price update (UTC):
Banggood (19.99 USD)
Banggood warehouse is located in China. I don’t think there is an active coupon right now – at least in my database. Good or bad price?
Link: Banggood product page
Price: 19.99 USD
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGGines, BG0dd754, BGTOOS729
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Aliexpress
Here are coupons that you can use.
Price history and price alert
Price history (for all/most countries) for WIFI Digital Wattmeter EU Plug 220V is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).