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 (56.30 USD): MVC8SPRING
Coupon (56.30 USD): 8BGwbg2204
(CouponsFromChina.com tip: put item in your cart and apply coupon code there 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): bgshOOp10, BGSAMRTH, BgcLuBofErtA10, BG15SH12, BGSTHO15, BGHONEY2110, BGSHOM15, BGSHE15, 13f142, BG57f09c, BGAQA929, BG4a7a54, ADMITAD2212, BGSmart6
(there’s a little possibility that old coupon will work)
Price history and price alert
Price history (for all/most countries) for Xiaomi Aqara EigenStone S2 ZigBee Smart Thermostat is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).