Hi,
I use and like an Ethernet SmoothStepper (ESS) by Warp9TD. I use two MB2 BoB's from Homann Designs in Australia but two C10's
are a reasonable alternative at $23 each or a C25 at $30, it has two ports worth of IO.
A more sophisticated BoB, 24V inputs/outputs, differential IO etc is the Mb3 from CNCRoom, made especially for the ESS.
Craig