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 coupon available! Pretty cool, huh?
Link: Banggood product page
Coupon (96.20 USD): BGherra
(CouponsFromChina.com tip: apply it in your 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): BG0224MD, 7d18f7
(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 MD-4060 Metal Detector is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).