Recommended device for testing my own SDR?
For both receive and transmit SDR experimentation/testing at RF/HF/VHF/etc. frequencies, I use a LimeSDR Mini (far less expensive than an Ettus). But I stream from/to it using C programs and files, not direct from Matlab.  (Is it possible to write a C stub to pass data back and forth with Matlab?)

There is also the ADALM-Pluto kit from Analog Devices, perhaps suitably priced for educational environments.  There seems to be some sort of Matlab support for it.

Some amateur radio transceivers (Icom, et.al.) have stereo soundcard (audio IQ) ports for conversion from/to (licensed) amateur radio frequency band RF.  

Added: Another solution for amateur radio HF band SDR experimentation is the Hermes Lite 2 open source kit transceiver