Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (374.99 USD): Email5
Coupon (374.99 USD): BGBX13YH
(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): BGBMAXS13, BGBX13SE, BGBXs13P, BGBXS13H, BGBX13S1, BGBX13S2, BGBX13S3, bGhOnEy10, BGTT10, BGBX13S4, BGBX13A, BGBXS13SF, BGBX13S5, BGBXS13KC, BGBX13S6, BGBX13S7, BGBX13S8, BGBX13S9, BGBX13MAX, BGBXS13UP, BG3633, BGBX13SH, BGBX13SK, BGBX13SS, BGBX13YR, BGBMX13US, BGBXS13LA, BGBMX13ES, BGBMX13RES, BGBXMS13
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Price history (for all/most countries) for Bmax S13 N4000 8/128GB is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).