There are dozens of options for radio, including kits that you could build yourself (some cases with 3d printing) and others that are all in one solutions. We will try to break down those options here.
Simple Options like the RAK Wireless WisMesh v2 will give you a turn key option to start using Meshtastic!
Another good option for a built-in node would be the LilyGo T-Echo. Also put together, it brings a low entry barrier to use and get started with Meshtastic.