What is everyone using for RFID?

I have a job that I'm working on that needs to have some RFID implemented.

I have some experience with RFID from past work, but not quite in this aspect.

Initially the project was going to be a single, large PLC to run the entire project. At the time, I was looking at Impinj Speedway units. The project has since drastically changed and each of the ~20 areas will now be controlled with their own smaller PLC (AD P1K, maybe BRX). Each area needs it's own locally connected RFID reader, making the Impinj units very, very costly.

Ideally I'm after a all in one type of unit, RS485, 125khz. ASCII or Modbus would be ideal. All I need is that when the tag is presented, it's read and I get the serial number of the tag.

Any thoughts?

We use a plant wide wifi network consisting of multiple buildings.
I would guess around 10 acres with 30-40 wifi access points.
the rfid scanners connect to the area wifi which then communicates to a central server in the server room. the server then sends data to the appropriate department, SQL table, or what ever is needed.

james