Aliexpress
Click here… to search for Xiaomi Piston Type-C Earphones on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (16.99 USD): BGAlerabatKL
Coupon (16.99 USD): BGAUDIO
(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
Old coupons (from the oldest to the newest): BGXMTYPE, TTxBG10, BGXMTYPE2, aff7off, BGTYPE, BG3CSUM, BGTYPEC, bgssaff9, AFfbG10, BGTC001, BGXMTC30, BGXMMTC, 502C6B, BGPISTONPL, BGPiston0109, BGVDay10%off, EARSP11, BGTT10, bGhOnEy10, BGXMTYE, 13f142, BGSS10%SW, bgshOOp10, BGELIG0920, BG11SHOP, BG4BW25, BGLOAC1, BGa0b145, BG725cc4, BGBuscape01, BGb952e7, BGBRPL2, BGHOTSHOP15, BG53e9c8, BGd173b4, BGAudioVideo
(there’s a little possibility that old coupon will work)
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi Piston Type-C Earphones.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).