I have checked all old coupons and price is $20.78 for SONOFF DUALR3 Dual Relay Module Switch (in Banggood). Basically copy coupon, view price history or create e-mail price alert. Let’s see what best price is ATM.
Enclosure Material: Fire-retardant ABS V0, Security Mechanism: WPA-PSK/WPA2-PSK, Gang: 2, Color: White, Max Current: 15A(total) /10A(1 gang), Humidity: 5%-95%RH / Non-condensing, Frequency: 802.11 b/g/n, Operating Temperature: -10ºC-40ºC, Product Dimensions: 54*49*24mm, Power Supply: 100-240V AC, Max Power: 3300W(total) / 2200W(1 gang)
Latest coupon and price update (UTC):
Banggood ($20.78)
Banggood warehouse is located in China. Coupons for SONOFF DUALR3 Dual Relay Module Switch? Nope, there’re no coupons in Banggood. Is it a low price? Well, this price is higher than average price ($11.94)
Link: Banggood product page
Price: $20.78
Old coupons (from the oldest to the newest): BGDUALR3, BGDUALR313, 13f142, BG36c08a, BGee1672, BG619c1a, 6GSGIT, ADMITAD2212, BGSmart6, 8Couponsde, MVC8SPRING, 8wEbgaInS5, pROMo8cuPoN, BGJUNEGSG9, BG15Sonoff, BG8ReviTrage, Cuponation9, 9OFFSUMMER, BG32140d
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – SONOFF DUALR3 Dual Relay Module Switch [EU] ($-3)
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Check out price history chart (for all/most countries) for SONOFF DUALR3 Dual Relay Module 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)).
. There are no coupons for this product in Banggood. I don’t want to misguide you about the price. I don’t know if it’s good, because I don’t have enough records in my database…