$13 for a tiny rx:
https://www.amazon.com/HGLRC-ELRS-2-4G-Receiver-Omni-Directional/dp/B0CNRX33V6that's about half the price of what frsky charges for their 10 year old tech. btw, frsky has at least 2 (maybe 3?) different protocols and its a nightmare if you have the wrong versions and want to inter-connect.
elrs even has a web interface if you need to change things (it can join your wifi network or be an AP and you connect to it).
its like comparing fortran to python. things have progressed quite a lot in rf remote control. just the richness of telemetry, alone, should make people consider converting.
and now, you have 'gemini' which is a pair of 900/2.4ghz diversity tx/rx pairs. so you can do really long range and also have a backup channel.
frsky is dead dead dead and they know it.
note, you used to need both a tx and rx line to run elrs (frsky needs only one serial line, usually). but now they added half duplex mode to elrs so if you must, you can get by with a single uart line, but its better if you have both tx/rx lines on your spare uart (on the plane).
finally, you probably need pwm outputs rather than 'serial' and you can find elrs rx's that break out directly into pwm servo ports. or you can use a single board to take elrs serial out (from its rx) and then that 2nd board will do the elrs_serial -> pwm for you. either way. you can get lots of pwms if you want. (also battery voltage telem, which is important!)