$29.99 – Output power: 25mW/500mW/1000mW/1600mW switchable, Cable connector: Solder pads, Weight: 11.3g(excluding antenna), 5V camera supply: 470mA(MAX)—-500mW@12V(Type), 5V camera supply: 550mA(MAX)—-1000mW@12V(Type), Antenna connector: MMCX, 30.5 stackable hole, Input voltage: 7V to 24V, Dimensions: 36mm*22mm*5mm, 5V camera supply: 830mA(MAX)—-1600mW@12V(Type), 5V camera supply: 220mA(MAX)—-25mW@12V(Type), Extra features: Smart audio, Power supply: 5V output for Camera.
I have just checked coupons. The lowest price I could get is $29.99 for Eachine TX805S 40CH 25/500/1000/1600mW AV RC FPV Transmitter (in Banggood). Basically copy coupon, view price history or create e-mail price alert. What is the best price?
Latest coupon code price check (UTC time):
Banggood ($29.99)
Banggood warehouse is located in China. I don’t think there is an active coupon right now – at least in my database. Low/high price? Hmmm, price is higher than average (which is $19.57 right now), so better set price alert down below…
Link: Banggood product page
Price: $29.99
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): BGETX805S, BGEach10, BGTX805S, BGTX8051, BGOTC21, BGTX80, BGTX805E, FBCOUPON1, BG11EACHINE, BGEachine2021, BGCuponation10, BGEachine10, BGRCEachine, Tabby20, BGRCT10, BGToys8, BGMatt2022, BG589b2e
(these coupons are old, so probably won’t work)
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.
Price history and price alert
Price history (for all/most countries) for Eachine TX805S 40CH 25/500/1000/1600mW AV RC FPV Transmitter is here. The lowest price was: $18.38.
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)).