The cost of sending promotional e-mails to a list of people who have asked to receive them is zero. Buy a list from a broker and you'll pay for each name and run the risk of being accused of spamming. But mailing to your own list of people who have asked to be notified of new developments is essentially free and tends to have a high return rate. A final example of an online marketing bargain is viral marketing. Viral marketing occurs when a seller notifies one prospect of an opportunity who then notifies several others who then notify several others.
Word spreads to a set of prospects that grows exponentially.
You've seen it happen with jokes being passed through e-mail. It happens as friends tell friends about cool sites. And it happens as friends tell friends about great online offers. When it happens, it happens fast and free. For nearly a decade the number of people using the Net has roughly doubled every year.