Aliexpress
Click here… to search for 12.5 Inch Android 9.0 Car Rear Seat Headrest Monitor on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. You can get coupon down below.
Link: Banggood product page
Coupon (298.44 USD): BGAUTO22
(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): BGCarAud1, BGCarAud3
(there’s a little possibility that old coupon will work)
Price history and price alert
Here is price history (for all/most countries) for 12.5 Inch Android 9.0 Car Rear Seat Headrest Monitor.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).