Price history, coupons and price alert are available on this page. You probably want to know what is the best price?
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
SONOFF M5 80 SwitchMan Smart Wall Switch APP Control Work with Alexa Google Home and Siri shortcut – 2 Gang
Banggood
Banggood warehouse is located in China. There is no active coupon in my database right now (for Banggood).
Link: Banggood product page
Price: $-3
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 and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG58024b, Cuponation9, BGsonoff30, BG8ReviTrage, BGa16d12
(there’s a little possibility that old coupon will work)
Price history and price alert
Check out price history chart (for all/most countries) for SONOFF M5 80 SwitchMan Smart Wall Switch.
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)).