Data I/O possibilities (closed) - Thanks
A Standard SiK radio set is the most common. Google “ardupilot sik radio”. Holybro and Mro make popular units.
You may find this page helpful:
Telemetry (landing page) — Copter documentation (ardupilot.org)
As Dave says, SiK radios are the most common and likely cheapest option (at least for any decent range).
No need to delete your posts and remove context from the title. Others may find the information useful.