Aliexpress
Click here… to search for Alldocube Expand X 13.3Inch 2K Monitor on Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. There is one coupon available! Pretty cool, huh?
Link: Banggood product page
Coupon (263.99 USD): 13f142
(CouponsFromChina.com tip: coupon code has to be applied in shop’s 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): 7d18f7, BGCuponation10
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for Alldocube Expand X 13.3Inch 2K Monitor.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).