So, what would you pay for a BOB that is setup for 8 motors with error feedback, spindle/vfd control, 6 high power outputs to drive disconnectors directly, probe-limits-encoder I/O, LCD display port, Hardware E-Stop, 2 Modbus RTU ports (slave or master), 2 high speed RS-422 ports, and 2 Microcontrollers with USB ports to program. An ESS mounts upside down on the BOB. Out of the box it will function like any other BOB, but when you program the micro-controllers you can make it do all sorts of fun stuff. All of the I/O signals are connected, not with screw terminals, but with shielded Cat5 connectors.
The reason I am building this board, is because I wanted to control a VFD using Modbus and have a Modbus attached pendant. The benefits of it is that all the logic I/O can be shielded and is balanced differential signaling so it is very resistant to RF noise.
My concept for this BOB was to make the ESS the interface to the Mach4 computer for timing critical signals but other external I/O would go through onboard micro-controllers and out to the world over standard industrial protocols.
The cost for the initial boards is in the $250 area, but that is before a size reduction which would include surface mounting all the components and optimizing for cost. I am not sure if I want to go to production on this yet, so we shall see. Here is a photo of my RS485 pendant and the PCB design (enlarged).
That's impressive. Sounds like you have it all figured out