Just check coupons out (with price alert and history). What is the best price?
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);
Aliexpress
There’re some similar (or not) items on Aliexpress
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. There is one coupon right now! Check this out.
Link: Banggood product page
1. ($17.18): ADMITAD2212
this code has to be applied in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): elec, BG15Gadgets, SONOFF15, bGpAnDacHeCk, BGVDay10%off, bGhOnEy10, BGSMOFF, BGSONOFF15, BGELIG0920, 13f142, BgcLuBofErtA10, BGSONOFF16, BGAFF10OFF, BGSTHO15, BGCuponation10, BGHONEY2110, BGSHOM15, BGSHE15, 6GSGIT, BG15Sonoff
(there’s a little possibility that old coupon will work)
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – SONOFF RF R3 Smart Switch [EU/UK] ($-3)
Price history and price alert
Do you need price history chart (for all/most countries) for SONOFF RF R3 Smart Switch? There we go.
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)).