Dimension: 51 × 44.5x 24mm, Working distance: Up to 50M in Open Space, Output: 100-240V~50/60Hz 16A Max, Battery model: CR2032, Work temperature: -10°C~40°C, Shell material: PC V0, Input: 100-240V~50/60Hz 16A Max.
Go down and check coupons out. Remember to check price history if it is available. What is best price?
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. I don’t think there is an active coupon right now – at least in my database.
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!
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): BGJUNEGSG9, BG15Sonoff, TTSUMMER8, Cuponation9, 9OFFSUMMER
(there’s a little possibility that old coupon will work)
Price history and price alert
Price history (for all/most countries) for SONOFF 100-240V 50/60Hz 16A S-MATE Smart Switch Module eWeLink is here. The lowest price was: $5.99.
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)).