Aliexpress
Click here… to search for Hubsan H109S X4 PRO Drone on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. Only one coupon available!
Link: Banggood product page
Coupon (412.87 USD): bGhOnEy10
(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)
Old coupons (from the oldest to the newest): TTxBG10, BGss35, AFfbG10, BGH109S10, BGBFAFF2019, BGCITYADS2019
(there’s a little possibility that old coupon will work)
Price history and price alert
Here is price history (for all/most countries) for Hubsan H109S X4 PRO Drone.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).