OPC-UA "black box" for 24v signals|Miscellaneous|Forum|OPC Foundation

I'm looking to standardize collection of 24v digital signals from various types of machines that do not have a PLC that we can connect to directly. Is there any "black box" type of hardware on the market that can take electrical inputs and export as OPC-UA with built-in UA server? A simple small PLC prebuilt with OPC-UA server and configurable inputs.

One option I am looking at is to use S7-1200 with Matrikon and define a standard interface like that, but it is more complicated as it requires a PC hardware in addition to the S7.

It is important to keep the total cost down.