Aliexpress
Click here… to search for Frsky R9M 2019 900MHz Long Range RC Transmitter R9 Slim+ on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. One coupon is available. Cool!
Link: Banggood product page
Coupon (67.97 USD): BGDAVIS
(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)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): 7d18f7, BGMD10, Parts8, BGR9MSWK, Email5, BGVDay10%off, BGR9MS, BGFrskyFB, BGTT10, bGhOnEy10
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Here is price history (for all/most countries) for Frsky R9M 2019 900MHz Long Range RC Transmitter R9 Slim+.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).