Aliexpress
Click here… to search for Jumper T8SG Lite RC Transmitter Yellow on Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (22.72 USD): BG50T8SGL
Coupon (36.35 USD): BGT8L20
Coupon (40.90 USD): BGBFAFF2019
Coupon (40.90 USD): BGCITYADS2019
Coupon (41.80 USD): Parts8
(CouponsFromChina.com tip: just apply this code 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): T8SG35, T8LT, 35OFFRSF, T8SGLT, BGT8LT, BGTL30, BGT8SGL, BGJPT8SGL, BGaDmITAd, BGJT8SGL
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Price history (for all/most countries) for Jumper T8SG Lite RC Transmitter Yellow is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).