Xiaomi Mijia 350mL Insulated Cup Vacuum Thermos (Banggood, Aliexpress: Cup Vacuum Thermos (the best price with coupon)).
Basically copy coupon, view price history or create e-mail price alert. Do you want to know what the best price is?
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($20.01): Cuponation9
2. ($20.23): BG8ReviTrage
3. ($20.67): BG00c906
paste coupon code in your cart and click Apply after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/feV
Old coupons (from the oldest to the newest): 00c906, BGe46870, BGAlerabat1, BG7280ff, Tabby20, 8Couponsde, BG36e006, MVC8SPRING, 8BGwbg2204, 2203ActiesNL, tRaDetRaCKeR, 8wEbgaInS5, BG2bb7a1, BG5d2ea4
(probably won’t work, but you can try them out)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi Mijia 350mL Insulated Cup Vacuum Thermos. The lowest price was: $15.99.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).