Consider this:
If we treated sound waves the way we treat radio waves, then by federal law, nobody else could speak in the same frequency range as my voice.
I could also buy all the sound frequencies I want, and nobody else, by federal law, would be ever allowed to speak when I am near, even if I am silent.
The reality is that when you buy radio bandwidth, you're not just buying yourself a megaphone, you're also buying away a piece of everyone else's right to speak. Real government forces, with guns, enforce that gag on the public for you.
So if this were a true free market, you could broadcast, but you wouldn't expect the taxpayers/government to stop everyone else from broadcasting just to preserve your monopoly of a frequency band.
Of course we need boundaries between frequencies, but we should stop fooling ourselves that the right to speak can be sold, without using oppression to create artificial scarcity.