Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (72.69 USD): BGAFF10OFF
Coupon (72.69 USD): bGhOnEy10
(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): BG0224MD, AFfbG10
(these coupons are old, so probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for MD-3010II Metal Detector with Earphones.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).