Just check coupons out (with price alert and history). Best price?
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):
Polyester, Polyester fiber, 10L, 340x 225x 130cm, 157g
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($16.55): BGTY704CP
2. ($16.55): BGCuponation10
3. ($16.55): BGAFF10OFF
coupon code has to be applied in shop’s cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): bGhOnEy10, BG458GH, BG10BPRA, BGXMNR1, BG569HJ, BGdragonBoat, BGCAMP01, BGHOTSALE4, BGEXPJL2, BGKHH9OU, BGRSKYBAG, bgshOOp10, BGSDJK23, BGFDSKL12, BgcLuBofErtA10, BGXMBAGG1, BGMMN, 35257c, BGSHHA, BGH5124, BGXM420, BGZPBC15, BG4d9120, BG00c906
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – Xiaomi 10L Starry Sky/Camouflage Backpack [EU] ($-3)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi 10L Camouflage Backpack.
Price records source(s): Gearbest, 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)).