Aliexpress
Click here… to search for Xiaomi Mi Drone 10 inch 4pcs Propeller 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 (14.16 USD): Parts8
Coupon (14.39 USD): 13f142
(CouponsFromChina.com tip: apply code in your basket (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): 502C6B, AESE, TTxBG10, 2019SPEDM, bgssaff9, AFfbG10, BGBFAFF2019, BGCITYADS2019, BGVDay10%off, BGAFF10OFF, bGhOnEy10, BGdragonBoat, BGSS10%SW, BGRC902, BgoFErTaSchInA10, BgcLuBofErtA10, BGCuponation10, BGHONEY2110, BGDAVIS
(these coupons are old, so probably won’t work)
Price history and price alert
Price history (for all/most countries) for Xiaomi Mi Drone 10 inch 4pcs Propeller is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).