You can create price alert here, copy coupons and view price history. What is the best price?
2.4G mode: AFHDS 2A, Failfe: Yes, Band width: 135, Frequency range: 2.408-2.475GHZ, Weight: 0.9 grams, Working current: 20MA, Output signal: PWM, Distance: 400+ meters, Channels: 4CH, Dimensions: 11 * 25MM, Receiver sensitivity: -92DBM, Supply voltage: 3.3-10V
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 and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($15.93): BGGAL8
2. ($15.93): BGRCParts8
coupon code has to be applied in shop’s 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): FS2A, 20OFFRSF, Parts8, BGaDmITAd, BGCITYADS2019, 2020CNY, BGVDay10%off, BGFS12, BGFKY11, bGhOnEy10, BGTT10, BGflysky11, BGRCRR9, BG11SHOP, 13f142, BGCuponation10, BGDAVIS, BG70e5fc
(these coupons are old, so probably won’t work)
Price history and price alert
Check out price history chart (for all/most countries) for FS2A 4CH AFHDS 2A Receiver.
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)).