Aliexpress
Click here… to search for MantisTek GM2 3500DPI Mouse on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. There is one great coupon!
Link: Banggood product page
Coupon (17.99 USD): 13f142
(CouponsFromChina.com tip: apply code in your basket (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): 215c65, f3e3a0, 502C6B, TTxBG10, e18b44, BGe28b38, AFfbG10
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Here is price history (for all/most countries) for MantisTek GM2 3500DPI Mouse.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).