It depends what you want to do:
Your original post looks like you may be asking how to access an AB PLC for free. You can license a copy of the Ignition OPC-UA server without any modules and use the quick client to read and write values to your AB PLC for free.
For data logging only SQL Bridge limited is $950.
From your OP I think you might also need the OPC-COM module for $350 to communicate with an OPC-DA server (if not using a 3rd party OPC-UA server like the free Ignition one, Kepware, etc).