Dring’s Grbl_ESP32 CNC Development Board is just $29, and is packed with features. You’ll need to supply your own NodeMCU ESP32 development board, and three stepper driver modules. But, that should cost less than $20 all-in. So, for less than $50 total, you’re getting a complete CNC controller that has more features than traditional Grbl controllers that cost a lot more.
Those features include the processing power of the ESP32 itself, WiFi and Bluetooth control, modular design, on-board connections for limit switches and the Z probe, and control switch connections for feed hold, cycle start, reset, and door. It also has PWM support for spindle speed, and connections for spindle enable and direction — which will be supported in firmware in the future. The board has a place for an SD card module, but that shares pins with mist coolant and spindle controls, so you may choose not to use it.
If you’re looking at building a CNC machine or want to replace the controller on an existing machine, this looks like a fantastic option. It’s more affordable than most control boards on the market, it’s open source, and it has a lot of potential for long-term use.