Great question! I totally understand the challenge of wanting to modernize without breaking the bank on a full system replacement. Here are some practical, cost-effective IIoT upgrade paths that can give you real-time monitoring while keeping your existing automation systems intact:

1. IIoT Gateway Solutions - These are your best bet for a quick win. Protocol gateways can connect your legacy PLCs and controllers to modern IIoT platforms, converting data from older protocols like Modbus or BACnet into formats that cloud systems can understand. They're relatively inexpensive and can be installed without disrupting your current operations.

2. Edge Computing Devices - Small edge devices can be added to process data locally before sending it to the cloud. This reduces bandwidth costs and provides real-time analytics right at your equipment. Many of these devices can connect directly to your existing PLCs and controllers.

3. Retrofit IIoT Sensors - Instead of replacing entire systems, you can add smart sensors to monitor key parameters like temperature, vibration, pressure, and energy consumption. These sensors gather real-time data and can communicate wirelessly to your monitoring platform.

4. Smart Communication Gateways - Some solutions combine HMI capabilities with data processing, allowing you to build an IIoT environment quickly while maintaining your existing control logic and programming.

The beauty of these approaches is that they let you maximize the value of your existing equipment while gradually introducing modern capabilities. You can start with critical equipment and expand as you see benefits, rather than committing to a massive capital expenditure upfront.