Maximum receive refresh rate: 500Hz, Frequency Range: 2400 MHz to 2500 MHz, Regulatory Domain: ISM2400, Weight: 50g (without antenna）, RF Output Power: ≤30dBm, Frsky Lite 8pin socket, Brand Name: Happymodel, MCU: ESP32(main) /ESP8285(as ESP backpack), Power supply voltage: 5v~12v, RF chip: SX1280IMLTRT, , Antenna gain: 1.87dBi, Dimension: 67.5mm*30mm*20.5mm (without antenna), Model: ES24TX Slim Pro, Minimum receiver refresh rate: 25Hz, Item Name: ES24TX Slim Pro Micro TX Module.
You can create price alert here, copy coupons and view price history. What is 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 coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. Well, there is one coupon available right now.
Link: Banggood product page
1. ($57.95): BGMatt2022
apply code in your basket (cart) after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/i1u
Old coupons (from the oldest to the newest): BG92a9c2, Parts8, BGRCParts8, Tabby20, BG1efeb0, MVC8SPRING, 8BGwbg2204, tRaDetRaCKeR, 8wEbgaInS5, pROMo8cuPoN, BG8RCToy, hoNEYbGdeAlS, BGRCT10, BGJUNEGSG9, BGRADIORU
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Price history and price alert
Here is price history (for all/most countries) for Happymodel ES24TX Slim Pro 2.4GHz ExpressLRS ELRS. The lowest price was: $48.99.
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)).