Aliexpress
Click here… to search for Tigernu T-B3164 21L 17 inch Backpack Gray on Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (55.14 USD): bgssaff9
Coupon (56.35 USD): aff7off
(CouponsFromChina.com tip: this code has to be applied in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Old coupons (from the oldest to the newest): 19BGTD, e2bcea, TTxBG10, BG3CSUM
(there’s a little possibility that old coupon will work)
Price history and price alert
Price history (for all/most countries) for Tigernu T-B3164 21L 17 inch Backpack Gray is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).