They are currently out of stock of the new FlexClass
BUT
This was 2 days ago, and it would probably be your best bet.
However, the FlexClass doesn’t do an “xClass” version, so if you were only wanting an xSeries. What you could do is grab a Mifare 1k test card, write the UID of you school ID to it, and see if that works.
If you don’t have a ProxMark3 to write to the test card, you could grab a Mifare 1k test card Gen 2, and use your phone to change the NUID.
If that works, you could grab an xM1 and a ProxMark3, the only real unknown from then is the coupling of the xM1 to your readers for a reliable read.
So you have a few options, you just need to decide which path you want to take.