I/O options

A couple years ago I did an old B&S mill with lcnc v2.5. I plugged into most of the original wiring and used 3 opto 22 pb24 g2 boards connected to a 5i20. This set up works well. The original wiring was pretty ruff and I'd like to rewire the machine. The opto boards are cumbersome and don't make for the neatest wiring job. I was looking at cost effective solutions for a replacement. I have 72 plus I/0 points. Inputs are 24vdc, outputs 110vac.

There are some options I'm aware of one is ssi from Mesa ( I already have an 7i44 in the system) . One is ether cat and the other is modbus. I'm not terribly famaliar with the later 2 . What are my options with the available drivers? What is most cost effective? Thanks