Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. I found coupon for you. Check this out.
Link: Banggood product page
Coupon (699.65 USD): BGRADIORU
(CouponsFromChina.com tip: 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
Price history and price alert
Check out price history chart (for all/most countries) for FrSky Tandem X20HD RC Transmitter ETHOS.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).