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 great coupon!
Link: Banggood product page
Coupon (342.99 USD): Email5
(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): Wholesale20, BGAnycubic1, bGpAnDacHeCk
(probably won’t work, but you can try them out)
Price history and price alert
Price history (for all/most countries) for Anycubic I3 MEGA 3D Printer EU Plug is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).