Making money with a 99-cent app requires massive, effective marketing. With very much under-powered marketing in the ’90s, I was able to make the equivalent of 2,058 App Store sales by selling [SpotLight] to just 10 people.

How many copies at 99 cents would you have to sell to make a good living? To make it easy, let’s say a good living is $100,000/year. To make that in revenue on a 99-cent app requires requires selling just over 144,000 copies per year.

This works out to about 394 copies every single day. Or 2,769 per week, or 12,000 per month.

To make a good living with SpotLight, I would have had to sell about 1,010 copies per year. Or 2.76 per day, or about 84 per month.

If I had sold 394 copies per day of SpotLight, I’d be over $100,000 some time on January 3.

Brent Simmons on the mechanics of cheap.

Once again, this is about the tech industry. But, yanno. Feel free to substitute (oh, just say) publishing instead.