Use coupon and get 5V ETFE for 22.49 USD (from Banggood). You can create price alert here, copy coupons and view price history. What is best price?
Latest coupon code price check (UTC time):
Banggood (22.49 USD)
Banggood warehouse is located in China. Isn’t it too expensive? Well, this price is higher than average price (20.41 USD) Well, there is one coupon available right now.
Link: Banggood product page
Price without coupon: 24.99 USD
Coupon (22.49 USD): BGAMMT03
(CouponsFromChina.com tip: put item in your cart and apply coupon code there after clicking “Proceed to checkout”. Click to copy code and open shop)
Old coupons (from the oldest to the newest): BGCarEle5, BG63715f, BGLMQ15, BGSCM11
(probably won’t work, but you can try them out)
Aliexpress
Click here… to search for 8W 5V ETFE Solar Panel on Aliexpress
Here are coupons that you can use.
Price history and price alert
Here is price history (for all/most countries) for 8W 5V ETFE Solar Panel.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).