Just check coupons out (with price alert and history). Do you want to know what the best price is?
, Card Extend: Up to 256GB external memory, RAM: 6GB LPDDR4X, CPU: Helio P70 (MT6771V/CT) / Octa-core / 4xCortexA73 /2.1GHz; 4xCortexA53 /2.0GHz, OS: Android 9, ROM: 128GB EMMC, GPU: ARM Mali G72 MP3 900MHz
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in Hong Kong.
Link: Banggood product page
1. ($400.39): Cuponation9
2. ($400.39): 9OFFSUMMER
apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): 8Couponsde, tRaDetRaCKeR
(there’s a little possibility that old coupon will work)
Price history and price alert
Check out price history chart (for all/most countries) for Blackview BV9800 Pro 6580mAh 6/128GB P70 with Thermal Camera.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).