Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (11.43 USD): BGLED07
Coupon (11.82 USD): Cuponation9
(CouponsFromChina.com tip: coupon code has to be applied in shop’s cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): Terence, BGLED2203, BG44d391, 8BGwbg2204
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Price history (for all/most countries) for 3W LED Solar Bulb Light Waterproof is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).