The latest is the TTGO T-Call, an ESP32 breakout board that also has a cellular modem. Yes, it’s only a 2G modem, but that still works in a lot of places, and the whole thing is $15. On board ...

It’s also a pretty safe bet you’d end up running it on some variation of the Arduino sitting in a motor controller breakout board ... to port Grbl to the ESP32 board. Price wise the Arduino ...