Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (408.19 USD): BGGAL8
Coupon (408.19 USD): BGJON8
(CouponsFromChina.com tip: apply it 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): Cholldrons68, BGMATT7, Drones6, BANGGOODSD, CouponsDE, 00c906, 8BGwbg2204
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Price history (for all/most countries) for Holybro Pixhawk 4 Mini QAV250 Completet Kit Drone is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).