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 and price update (UTC):
Banggood
Banggood warehouse is located in China. I am tired of searching coupons, but I found one for you…
Link: Banggood product page
Coupon (298.44 USD): BGAUTO22
(CouponsFromChina.com tip: you should apply the coupon 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
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
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).