Some basics:
Economics
In selling things, we can divide costs into fixed and marginal. Marginal cost is the extra expense incurred by selling one more thing, while fixed costs are independent of how many things are sold. By subtracting marginal costs from total revenue, we get the marginal revenue (not as standard a term), and costs are normally set to maximize that. By subtracting fixed costs from marginal revenue, we get profit or loss.
Setting prices is normally done to maximize marginal revenue (high prices mean high revenues for few sales, low prices mean lower revenues for more sales). Further, companies are normally greedy, since they're normally rated on profits. Therefore, high prices are not because a company wants more money (they all do), but because that's the price that makes the company the most money. Similarly, companies can't just raise prices to make up for costs or anything else, since if they're doing things right that will reduce their profitability.
Traditional manufacturing
Traditionally, the economy has been based on selling tangible things, even when it appeared otherwise. Newspapers were good at selling packages of cheap paper with news printed on it, not news itself. The secret of being successful was to make and sell things at low cost, and sell at higher prices. In a competitive environment, the market price of something was based on its marginal cost, and it was stable because the manufacturers could make things less expensively than their competitors or customers. This is what most people's ideas of a market economy are based on.
Information Economy
The main difference is that information, in various forms, can be reproduced at almost no cost, both by the original manufacturer and the customer. By conventional market standards, above, this means that the price of music or software or other such things should be approximately zero. The other major effect is that valuable things can be easily copied, so somebody who wants a copy can get one without depriving anybody else of theirs. Indeed, if what is copied has value, then making additional copies, with or without anybody's permission, increases total wealth.
Another effect has been the breakdown of media channels. "Channels" was a good word, because it implied constriction and potential control. When I was younger, the easiest way for me to get access to the AP news feed was to buy a newspaper and read what they printed of it. Today, I have direct access from my phone, so the easiest way is to take my phone out of my pocket.
Music sales, for example, have been affected by both those main effects. It used to be that a music company could manufacture an object containing music much less expensively than I could, and I had no way of getting the music off the object except simply listening to it. This meant that I had to get music from record companies. Today, I can make copies of music easily, and I can get such copies from many sources.
Copyright
The solution to free copying was originally copyright. As long as marginal costs remained significant, and media channels ruled, it was fairly simple. Anybody seeking to make copies in any significant quantity required expensive equipment, and any attempt to make money by selling large numbers of properties could be caught and prosecuted. There was no need to worry about individual copies, since they weren't economically significant.
The legal basis for copyright in the US is the provision of a monopoly for a limited time to encourage people to create things. (I've seen no evidence that this was considered as any sort of property back then.) Copyrights that make it easier to profit from creative work have two desirable features: they allow sufficiently good artists to concentrate on their art, and they provide financial incentive for creating.
