$8.99 – 2 Transmitters with 12V 4CH Channel Relay RF (Banggood, Aliexpress: Remote Distance: 30M, Receiver sensitivity: 105dB, Operating Voltage: DC 12V, Receiving frequency: 443.92MHz, Max load current: 20A, Frequency: 315mhz, Operating Current: 13 mAh (the best price with coupon)).
ATM you can buy 2 Transmitters with 12V 4CH Channel Relay RF for $8.99 (in Banggood). You can create price alert here, copy coupons and view price history. What is best price?
Latest price update (UTC time):
Banggood ($8.99)
Banggood warehouse is located in China. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood. The question is – is it a good price? Current price is the lowest in history (according to CouponsFromChina database)!
Link: Banggood product page
Price: $8.99
This is the best price ever noted in my database!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG1d6233, BG00c906, BG589b2e, BGET10
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
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
Price history (for all/most countries) for 2 Transmitters with 12V 4CH Channel Relay RF is here. The lowest price was: $8.99.
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)).