Aliexpress
Click here… to search for Graupner GM X-8N RC Transmitter on Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. Well, there is one coupon available right now.
Link: Banggood product page
Coupon (227.46 USD): Parts8
(CouponsFromChina.com tip: paste coupon code in your cart and click Apply after clicking “Proceed to checkout”. Click to copy code and open shop)
Old coupons (from the oldest to the newest): BGGMX8N, BG10PARTS, BGAFF10OFF, BGTT10, bGhOnEy10, BGdragonBoat, BGSS10%SW, bgshOOp10, BGRC902, BgoFErTaSchInA10, BgcLuBofErtA10, BGCuponation10, BGDAVIS, BGHONEY2110
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Do you need price history chart (for all/most countries) for Graupner GM X-8N RC Transmitter? There we go.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).