This article in the Wall Street Journal draws a lot of parallels between today's app makers and the Tin Pan Alley musicians--there's a big market and barriers to entry are low. The problem is getting people to notice you. (Hey, notice any parallels between those two businesses and a certain third?)
Marketing and selling the app remains a crude undertaking. It's still difficult for users to discover new apps much beyond Apple's "Top 10" lists. As in Tin Pan Alley, a mercenary world of gimmickry and "hit-making" middlemen promise to push an app onto these charts. Song-plugging has even returned. Today it's called "pay per install"—in which app developers pay anywhere from a quarter to a few dollars for each app download....
Typical costs now run roughly $1.50 to $1.80 per installation, a stiff sum for a free or 99-cent app. Games companies are now spending 60% to 70% of their gross income on this marketing, he says.
It's both interesting and a kind of cautionary tale: There's pressure to lower prices in the face of all the other products (a pressure that I think is more intense because people are cranking out "me-too" apps by the dozen, and the only way for those to stand out is by being cheap), but if you lower your prices too much, any money spent marketing will necessarily be a complete loss.