Aliexpress
Click here… to search for 30.5×30.5mm Skystars 3-6S Stack F722 Flight Controller 45A/60A 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 (95.62 USD): BGGAL8
Coupon (95.62 USD): BGJON8
Coupon (95.62 USD): BGRCParts8
(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): BGESF745, Parts8
(these coupons are old, so probably won’t work)
Price history and price alert
Price history (for all/most countries) for 30.5×30.5mm Skystars 3-6S Stack F722 Flight Controller 45A/60A is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).