Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (12.77 USD): BGAFF10OFF
Coupon (12.77 USD): BGTT10
Coupon (12.77 USD): bGhOnEy10
Coupon (13.19 USD): 13f142
(CouponsFromChina.com tip: just apply this code 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): BGTCLB, AFfbG10, BGGRTCL, BGTECBAG01, BGBFCR29, BGBFTCL, BGCITYADS2019, bGpAnDacHeCk, BGVDay10%off
(there’s a little possibility that old coupon will work)
Price history and price alert
Price history (for all/most countries) for Teclast 15.6-inch Laptop Backpack is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).