You will find that for PLC's with the small I/O count that you require, few models from any manufacturer will have ethernet/modubus combination (or cheap, but I may soon be wrong!), maybe RS-485 based network would be a cheaper option for you in this regard?

Alternatively, if you find that you can service all your control needs from one PLC, but your I/O needs to be distributed over long distances, then one PLC with 'remote I/O' slaves (with ethernet or RS485) maybe a better option (well, easier to program at the syetem level IMO).

Of course, your operational requirements, along with the hardware specs, will determine the final cost of the actual hardware.

Also the IEC-1131 standard allows for up to five different languages including structured text. Unfortunately, it doesn't resemble C in any real sense, more like basic or pascal.

Please note however this information is only accurate as of July 2006, when I left the Automation industry :)


Valentin