Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. You can get coupon down below.
Link: Banggood product page
Coupon (26.61 USD): 13f142
(CouponsFromChina.com tip: apply it in your 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): BGC51671, AFfbG10, BGMST32, BGHOMEG12, FBCOUPON1, BGHome15%, BGHOMEA15%, BGAFF10OFF, BGCuponation10
(there’s a little possibility that old coupon will work)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi Youpin Solista 320mL Vacuum Cup.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).