According to my DB the lowest price is $7.25 for 20L Foldable Backpack Ultralight (in Banggood). Get coupons, create price alert or check price history out! Let’s see what best price is ATM.
20L Foldable Backpack Ultralight Outdoor Folding Backpack Travel Daypack Bag Packable Sports Bag for Men Women – Black
Latest coupon code price check (UTC time):
Banggood ($7.25)
Banggood warehouse is located in China. I don’t think there is an active coupon right now – at least in my database. Price? This price is higher than average price ($6.42) for this item.
Link: Banggood product page
Price: $7.25
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG3661a0, Sports23q1, BG589b2e, BG4a87be, BG4844f4, BG1cb589, BGc28268
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Price history (for all/most countries) for 20L Foldable Backpack Ultralight is here.
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)).