Aliexpress
Click here… to search for Xiaomi AIRPOP Posture Corrector on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. I found coupon for you. Check this out.
Link: Banggood product page
Coupon (43.99 USD): 13f142
(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)
Old coupons (from the oldest to the newest): BGHealth, ML15%Pro, vipupgrade8, BGMIB2, aff7off, BGBS20, BGbeauty001, bgshOOp10, BGHB20, bGhOnEy10, BgoFErTaSchInA10, BgcLuBofErtA10, BGCuponation10
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi AIRPOP Posture Corrector.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).