Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. There is one great coupon!
Link: Banggood product page
Coupon (52.73 USD): BGDAVIS
(CouponsFromChina.com tip: put item in your cart and apply coupon code there 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): AFfbG10, BGGEPPart, BGVDay10%off, bGhOnEy10, BGAFF10OFF, BGdragonBoat, BGSS10%SW, bgshOOp10, BGRC902, BgoFErTaSchInA10, BgcLuBofErtA10, BGCuponation10
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Check out price history chart (for all/most countries) for HGLRC FD435 Stack FD F4 Mini RC Flight Controller 35A.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).