Telemetry Interface: Smart Port, External Power Supply: 6V~13V, Compatibility: R9 Series Receivers, Modulations: PXX or CPPM (auto-detected), Vin Voltage Range: 6V-13V, Item Name: R9M 2019 900MHz Transmitter Module, Upgrade Interface: Smart Port.
Just check coupons out (with price alert and history). Best price?
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. I found coupon for you. Check this out.
Link: Banggood product page
1. ($67.97): BGDAVIS
apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): 7d18f7, BGMD10, Parts8, BGR9MSWK, Email5, BGVDay10%off, BGR9MS, BGFrskyFB, BGTT10, bGhOnEy10
(probably won’t work, but you can try them out)
Price history and price alert
Price history (for all/most countries) for Frsky R9M 2019 900MHz Long Range RC Transmitter R9 Slim+ is here. The lowest price was: $61.59.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).