RF design is very much an art, and the difference between works and works really well without harmonics and noise is a matter of design subtleties and often expensive parts. There are decent SDR setups around $500-700 that are known to be pretty good, but you have to go out of your way to buy them from the actual design houses, because despite being “identical”, the clones are not the same. In RF, the devil is in the details.
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.
