You can sometimes find a good deal on a HackRF as well. It has a freq range of 1mhz to 6ghz (rx/tx). The popular RTL-SDR only has 0.5mhz to 1.7ghz freq range (rx), but costs only about 1/4.
If you're okay with (1) not supporting the guy that designed it in the first place and (2) taking a risk on a Chinese knock-off (reviews generally seem good), you can often find the Hackrf One on the usual suspect sites straight from China relatively cheaply.
There's a listing right now for just the hackrf one board at $125USD (versus a legit one at $350USD).
Hate to say it but I ordered one from there (with a metal case, high stability clock, assortment of antennas and other useful stuff) for $160.
I've had my eye on one for years, but it's just never going to be something I'm willing to drop $350+ on as part of the hobby.
I don't think you can really call them a knockoff. As far as I know, the HackRF has been designed as an opensource hardware[0], so I'd guess the designer intended it to be built by different entities.
There's a listing right now for just the hackrf one board at $125USD (versus a legit one at $350USD).
Hate to say it but I ordered one from there (with a metal case, high stability clock, assortment of antennas and other useful stuff) for $160.
I've had my eye on one for years, but it's just never going to be something I'm willing to drop $350+ on as part of the hobby.