How much does it cost Wikipedia to have one more person read an article? How much does it cost Chanel to produce one more bottle of perfume? How about one more digital copy of a Grateful Dead concert?
The cost of the next item produced is called 'marginal cost'. It doesn't include set-up fees, rent, years of training, insurance or all the other huge costs an organization might pay. It's merely the cost of one more unit.
In a competitive, undifferentiated market, the price will generally be lowered by competitors until it is just above marginal cost. Think about that... If it costs a dollar to make something, and your competitor is selling for $1.10, then in an efficient market, you have every incentive to sell your item for a penny less than that. It's better than not selling it.
There are many implications of this, the first being the explanation of why so much stuff online is free. Free is a magical concept, the place where trial and virality live. If the marginal cost of a new user is virtually zero (and in an ad supported business, a new user is actually profitable, not a cost) then it's no surprise that it's hard to charge for your app when there are other apps that do precisely what yours does.
Big, established companies have traditionally had a difficult time understanding this concept. The market for ebooks, for example, ended up in Federal court because otherwise smart people in book publishing couldn't get their arms around the idea that their marginal cost of an ebook delivered by Amazon was precisely zero. No paper, no shipping, no ink.
Their response was to talk about all of their fixed costs (which are real, and which are important). Things like typesetting and advances and editing and promotion...
But none of those things are marginal costs. That means that someone entering the market, someone with nothing to lose, is happy to wipe out as many fixed costs as he can and then price as close to zero as he can get away with. It's not nice nor does it feel fair, but it's true and it works.
The only defense against this race to marginal cost is to have a product that is differentiated, that has no substitute, that is worth asking for by name.
If your product has a low marginal cost and a traditionally high price, particularly if it's one of a kind in its market, then you're in a great position to benefit from sampling. Which is why vodka companies are happy to sponsor parties and why cell phone companies will do almost anything to get you in the door.
Until you understand the true marginal cost of your products or services, you can't make smart decisions about pricing or customer acquisition.
Industries with zero marginal-cost products and services are inherently unstable until someone figures out how to become the king of the hill, the leader, the one worth picking because everyone else is. When that happens, the truth above about efficient markets goes away... because a market with one dominant leader isn't efficient any more.