Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. There is one great coupon!
Link: Banggood product page
Coupon (2684.40 USD): Terence
(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)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGT113, BgcLuBofErtA10, bGhOnEy10, BGAFF10OFF, BGT1100M, 7bcdf9, BGCuponation10, BGHONEY2110, BGMATT7, 2022ACTIESNL
(these coupons are old, so probably won’t work)
Price history and price alert
Check out price history chart (for all/most countries) for Poseidon GENEINNO T1 100m Underwater RC Robot.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).