I couldn't find it anywhere else, so I went and made a library with a very simple interface to an ID-12/20 RFID reader.
I thought i'd go ahead and post about it here in case anyone else is interested in using it.
So far I've only been able to test this on an Arduino Uno. If anyone has different hardware that they can test it on I would very much appreciate that.
Here's a video describing the full setup process:
And here's a link to the library itself: https://github.com/Thumperrr/Arduino_ID20Reader
Any feedback is appreciated!