Firefly 8S Remote Controller (Banggood, Aliexpress: for 8S / YI 4K Action Camera, Bluetooth 3.0, Working distance: 10m, Replaceable single 3V CR1632 cell battery (the best price with coupon)).
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.
Link: Banggood product page
1. ($8.12): e2bcea
2. ($8.12): 502C6B
3. ($8.79): rchobbies8
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/feV
Price history and price alert
Price history (for all/most countries) for Firefly 8S Remote Controller is here. The lowest price was: $3.99.
Price records source(s): Gearbest, 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)).