Remote Modbus I/O
G3 Technologies in Louisburg, Kansas has a line of remote I/O that looks interesting. The entry level product is a the Model G301, which provides 36 I/O points in a bare-board package.
From the web site: The Model G301 RIO (Remote I/O) is a low cost solution for I/O expansion and remote I/O requirements in SCADA and Process Control applications. It provides 24 Digital Inputs, 4 Analog Inputs, and 8 Digital (FET) Outputs. See pdf data sheet for details, and call G3 Technologies for pricing.
The G301 uses standard RS485 serial data communications with Modbus Slave protocol. It is especially suited for applications requiring low power and/or environmental tolerance, including SOLAR applications. It also makes a great local or remote “Modbus End Device” to gather data for a PLC or RTU acting as a Data Concentrator.