Wireless Standard: IEEE 802.11 b/g/n 2.4GHz, Enclosure Material: ABS V0;, Max Power: 2200W;, 433.92MHZ;, Power Supply: AC 100-240V;, Max Current: 10A;, Gang: 1;, Product Dimensions: 91*43*25(mm);.
Price history, coupons and price alert are available on this page. Let’s see what best price is ATM.
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 price update (UTC time):
Banggood
Banggood warehouse is located in China. I found coupon for you. Check this out.
Link: Banggood product page
1. ($17.18): ADMITAD2212
just apply this code in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/i1u
Old coupons (from the oldest to the newest): elec, BG15Gadgets, SONOFF15, bGpAnDacHeCk, BGVDay10%off, bGhOnEy10, BGSMOFF, BGSONOFF15, BGELIG0920, 13f142, BgcLuBofErtA10, BGSONOFF16, BGAFF10OFF, BGSTHO15, BGCuponation10, BGHONEY2110, BGSHOM15, BGSHE15, 6GSGIT, BG15Sonoff
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – SONOFF RF R3 Smart Switch [EU/UK] ($-3)
Price history and price alert
Here is price history (for all/most countries) for SONOFF RF R3 Smart Switch. The lowest price was: $7.19.
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)).