Before you begin a direct mail campaign, try some basic arithmetic first. A received a phone call last month from a potential direct mailer who had a $20 retail product, targeted to computer users. Each product cost $14 to produce, which left a gross profit of $6/each. Space advertising in national computer publications was way too expensive. Direct mail seemed a better alternative. But a basic direct mail package, including list costs, printing, mailshop expenses, etc. costs an average 33 cents each in the mail. Using a base price of $33/hundred, we'd have to gain a 5.5% response just to break even on the mailing costs. While a high response is certainly possible, I couldn't recommend a direct mail campaign to individual computer users and honestly expect my client to stay out of Chapter 11.
Rather than marketing directly to consumers, I recommended (a) offering the product via direct mail to computer user groups for combined group purchases, (b) offering the product to manufacturers and businesses as premiums and gifts, and (c) advertising in local computer users groups' newsletters (low cost ads + high market penetration in a trusted publication = high response and profit per ad dollar.
Direct mail is a highly effective advertising method, but sometimes it doesn't make sense. I recommend you always look before you leap into any advertising program. Sometimes the leap isn't worth the effort.