Aliexpress
Click here… to search for 12pcs JJRC JJPRO-3545BN 2-blade RC Propeller on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. One coupon is available. Cool!
Link: Banggood product page
Coupon (4.76 USD): BGMatt2022
(CouponsFromChina.com tip: coupon code has to be applied in shop’s 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): BGcc2861, BGToys8, BG25d4e7
(these coupons are old, so probably won’t work)
Price history and price alert
Price history (for all/most countries) for 12pcs JJRC JJPRO-3545BN 2-blade RC Propeller is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).