Aliexpress
Click here… to search for FrSky XSR 2.4GHz 16CH ACCST Receiver on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (15.46 USD): BGaDmITAd
Coupon (15.63 USD): Parts8
(CouponsFromChina.com tip: apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Old coupons (from the oldest to the newest): FRXSR, 20OFFRSF, 502C6B, 10Frsky, BGFrXSR, BGXSR12
(probably won’t work, but you can try them out)
Price history and price alert
Check out price history chart (for all/most countries) for FrSky XSR 2.4GHz 16CH ACCST Receiver.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).