Aliexpress
Here are coupons that you can use.
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – 5V/7-28V Power Supply 8 Channel ESP8266 WIFI 8-way Relay Module ESP-12F [EU] (-3 USD)
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. Well, there is one coupon available right now.
Link: Banggood product page
Coupon (15.12 USD): BG00c906
(CouponsFromChina.com tip: apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): ADMITAD2212, 2022ACTIESNL, Terence, 8Couponsde, MVC8SPRING, BGJUNEGSG9, TTSUMMER8, Cuponation9, BG589b2e
(these codes were not working in latest coupon update, but you can check them out anyway)
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – 5V/7-28V Power Supply 8 Channel ESP8266 WIFI 8-way Relay Module ESP-12F [EU] (-3 USD)
Price history and price alert
Here is price history (for all/most countries) for 5V/7-28V Power Supply 8 Channel ESP8266 WIFI 8-way Relay Module ESP-12F.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).