$21.69 – 13W Portable Solar Panel Kit 5V (Banggood, Aliexpress: Working voltage: 5V, Product net weight: about 155G/160G/265G, Material: Class A polycrystalline silicon solar panel, Output: Dual USB, Power: 6W/10W.60W (the best price with coupon)).
You can get 13W Portable Solar Panel Kit 5V for $21.69 using coupon code (in Banggood). Basically copy coupon, view price history or create e-mail price alert. Do you want to know what the best price is?
Latest coupon and price update (UTC):
Banggood ($21.69)
Banggood warehouse is located in China. Too bad there’s no coupon right now in Banggood. Is it cheap? From what I can see this price is higher than average price ($20.63).
Link: Banggood product page
Price: $21.69
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG589b2e, BGd2f208, BGET12, BGET10
(these coupons are old, so probably won’t work)
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 13W Portable Solar Panel Kit 5V is here. The lowest price was: $19.52.
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)).