RFID Login On Mobile Devices

I have been searching for a good way to implement RFID badge scanning on mobile devices (specifically iOS and Android tablets) but have not had much success. I know Zebra makes sleds (for hand-held devices) that can be adapted with a special case, but those seem cumbersome and very expensive (I potentially need 200+). I have also seen peripheral Bluetooth devices, but I don't see that as a viable option for a manufacturing operation.

The only other option I can see at the moment is to have a "base station" with an Ignition app that would assign the user to that specific device. This idea sort of works but isn't super practical for our locations that have large footprints.

I'm curious if anyone else has implemented something similar or has some advice.
Thanks