Well, having just been browsing I was looking at Ethernet (as it is one thing I understand)

My spindle is controlled via a serial port and a plug-in so that is one thing I don't need to worry about.

Saving up is not an option as having the router misbehave is costing me money, so having just spoken to my pension provider it is time to start planning.

By my reckoning I need:
1) an Ethernet based motion controller
2) a connection block and cable to the controller
3) PSU
4) 3 drivers

Mount all these on a board, (now it gets tricky) connect the outputs from the current drivers and the limit switches/probe switch to '#2. Rip out everything from the control box and install the new setup.