Aliexpress
Click here… to search for H11 2.4G 4CH RC Boat on Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. Only one coupon available!
Link: Banggood product page
Coupon (23.99 USD): BGd063e9
(CouponsFromChina.com tip: apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Old coupons (from the oldest to the newest): BG6643bb, BGb2283b, BG96f4d9
(probably won’t work, but you can try them out)
Price history and price alert
Here is price history (for all/most countries) for H11 2.4G 4CH RC Boat.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).