Aliexpress
Click here… to search for HGLRC FD413-VTX 16×16 F411 Flight Controller 13A 2-4S on 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 (51.59 USD): BGAFF10OFF
Coupon (51.59 USD): BGCuponation10
(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): BGdragonBoat, BGSS10%SW, bGhOnEy10, bgshOOp10, BGRC902, BgoFErTaSchInA10, BgcLuBofErtA10
(there’s a little possibility that old coupon will work)
Price history and price alert
Price history (for all/most countries) for HGLRC FD413-VTX 16×16 F411 Flight Controller 13A 2-4S is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).