I like my HackRFOne, but be aware it's half-duplex, so it can transmit as well as receive - but can only do one of them at a time. For a little more money you can get full duplex SDRs, which opens up a bunch of extra interesting sttuff you can do.

Do the hackRF folks make a more advanced one? I used to know of a good one around $600 but I can’t seem to remember it.