Basically copy coupon, view price history or create e-mail price alert. Best price?
Battery: 1x 3.7V / 1200mAh 18650 Li-ion battery (included), Solar panel: 5V / 1W, polycrystalline silicon, 500LM, IP65
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):
Price history and price alert
Price history (for all/most countries) for Utorch Waterproof Solar Induction Light is here.
Price records source(s): Gearbest
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)).