EmonBase is usually referred to as being an RFP69Pi card on a RaspberryPi so the EmonTX and EmonBase communicate via RFM.
A third option is an EmonTX wired directly to an RPi.
- EmonTX -> RFM -> EmonBase (Emoncms on EmonBase)
- EmonTX -> EmonESP -> WiFi -> Emoncms
- EmonTX -> Serial/wired -> RPi (Emoncms on RPi)
The difference is how you then host or manage the data from the EmonTX. With option 2 you need another device somewhere hosting Emoncms or just use emoncms.org.
Option 3 is the cheapest, but needs some user effort to do the wiring. If you search the forum, you will find several options for the serial connected version.