Just check coupons out (with price alert and history). Do you want to know what the best price is?
Capacity: 80L
Aliexpress
I could not find it 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 Europe 
. I don’t really know if this price is reasonable, coz there’s no price history in my DB. There is one coupon right now! Check this out.
Link: Banggood product page
1. ($50.23): BGc363fd
paste coupon code in your cart and click Apply after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGAFF10OFF, BGBAG80, BG146151, BgcLuBofErtA10, BGZPBC15, BGTY704CP, BGCuponation10, BGHONEY2110, BG10OFFAFF, BGwhielabel, BGBWITHUS143, 13f142, BG10OFFAFF1, BG281e4d, BG4d9120, BGAlerabatod, BG00c906, BG36e006, MVC8SPRING, 8BGwbg2204, tRaDetRaCKeR, BG2bb7a1, BG5d2ea4, BG8ReviTrage, Cuponation9, BG073996, BGc5e1ec, BG8OFFCOUPON, TTBLACK5, BG589b2e, BGSaleFeb8, BG781363, BGc28268, BG9dce6b
(these codes were not working in latest coupon update, but you can check them out anyway)
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. China – IPRee 80L Waterproof Hiking Backpack ($-3)
Price history and price alert
It doesn’t make sense to generate price history chart, because there is one price record which is: $39.99.
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)).