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 (205.15 USD): BANGGOODSD
Coupon (207.35 USD): Drones6
(CouponsFromChina.com tip: you should apply the coupon in your 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): bGpAnDacHeCk, AFfbG10, BGGEPDolphin, BGDOL153, BGVDay10%off, BGDOL2, BGAFF10OFF, bGhOnEy10, BGdragonBoat, BGSS10%SW, BGDolphinP, bgshOOp10, BGRC902, BgoFErTaSchInA10, BGHALLOWEEN, BgcLuBofErtA10, BGDolphinAA, BGDolphinBF, 7bcdf9, BG10RACING, BGCuponation10, BGMATT7, BGDAVIS
(these coupons are old, so probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for GEPRC Dolphin 153mm 4S Drone PNP.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).