Software Defined Radio may presently be used in the following ways:
1. On-Site SDR-Components including the SDR and frequency conversion units wired to an antenna, and connected to a computer.
2. Remote SDR-Components built and maintained by others and made available via an Internet-Browser for a few users simultaneously.
The first will cost from $50 to $100, depending on how you connect it, with at least half the cost being for the antenna and supporting cabling.
The second one is basically free of any investment of money, but limited by the capacity of the browsed SDR-Site. Typically from 4 to a dozen users individually controlling the received frequencies.
See details at sdr-components and instructions via the sdr-videos