Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. There is one coupon available! Pretty cool, huh?
Link: Banggood product page
Coupon (44.57 USD): BANGGOODSD
(CouponsFromChina.com tip: just apply this code 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): 13f142, BGHONEY2110
(there’s a little possibility that old coupon will work)
Price history and price alert
Check out price history chart (for all/most countries) for 250x420x3mm 3K Black Carbon Fiber Plate.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).