Aliexpress
Click here… to search for JX Servo PDI-2004MG 4.2Kg Metal Gear Digital Servo on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (19.03 USD): BGMatt2022
Coupon (19.03 USD): BGToys8
(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)
Old coupons (from the oldest to the newest): BG2e3f59, Cuponation9
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for JX Servo PDI-2004MG 4.2Kg Metal Gear Digital Servo.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).