Effective antennas are reasonably easy to build from scratch (depending on the frequency band), and are commercially available in an insane number of variations

Effective antennas are reasonably easy to build from scratch (depending on the frequency band), and are commercially available in an insane number of variations. Either way is very cheap - as little as a few dollars. Software defined radios can be had for as little as $10-20 for simple receive only types, up to several hundred for substantially nicer transceivers. They can also be $1000+ for special applications or R&D.