pole around 929.600mhz and you'll eventually find a shitload of phi in most metro areas. you'll probably also find a ton of industrial traffic, and the occasional weather and sports scores.
it's also not far fetched to think it's used as a means to broadcast to/from field operatives. most pager lines offer an smtp gateway, so a bit of "spam" could have a intended recipient anywhere in the region, or possibly country based on network.
One time I had my audio misconfigured to use my microphone instead of the line-in, and I had my radio disconnected from the computer to tune the antenna. As I was listening through the radio's built-in speaker, my computer properly decoded a number of FT8 transmissions... through the microphone. You really don't need anything expensive or interesting to do SDR stuff on the HF bands.
People that buy the "real" ham SDRs are doing things like contesting, where they really need to see entire bands, or even multiple bands, at once. And they're paying over $10,000 for that.
The cheap "hacker" SDRs are largely inadequate for ham work. They are OK, but not great. They don't have proper frontends, so transmit a lot of out-of-band garbage. They don't have niceties like an antenna matching network, or even a power amplifier. I have a KX3 which has a maximum transmit power of 12W. But these hobbyist boards will max out in the mW range. It is adequate for some digital modes, but even then, it's pretty low. I typically run FT8 at 1-3W. So generally, would not recommend these for someone new to the hobby. Buy an RTL-SDR stick for $20. Listen to some stuff. When you get bored, find a proper HF radio in the $300 range and use that. If you then decide you want to spend $10,000 on the hobby, then you can start looking into the SDRs ;)
A much less costly (but still highly flexible) option is to combine a high-performance SDR receiver from Elad or SDRPlay with a conventional transceiver. A T/R switch like the MFJ-1708SDR will protect your SDR receiver when you key up, while CAT control allows both rigs to be operated from the same software.