Xiaomi HUOHOU Vacuum Bottle Stopper (Banggood, Aliexpress: Color Black, Size Vacuum Stopper: 40x 70mm, Outer Material Stainless Steel, Weight 20g, Inner Material Silicone (the best price with coupon)).
You can create price alert here, copy coupons and view price history. Let’s see what best price is ATM.
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($13.95): Terence
2. ($14.10): BG00c906
apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/i1u
Old coupons (from the oldest to the newest): BGMS79K, AFfbG10, BGVDay10%off, BGHOMEG12, BGstpp25, 13f142, BGAFF10OFF, bGhOnEy10, BGdragonBoat, BGSS10%SW, bgshOOp10, BGHome15%, BGHOMEA15%, BGNOFR185, BgcLuBofErtA10, BGJATD185, BGCuponation10, BGHONEY2110, BG10OFFAFF, BGwhielabel, BGZXJU185, BG10OFFAFF1, BANGGOODSD, BGAlerabat1
(these coupons are old, so probably won’t work)
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi HUOHOU Vacuum Bottle Stopper. The lowest price was: $6.99.
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)).