From Byron Acohido and Jon Swartz’s “Going price for network of zombie PCs: $2,000-$3,000” (USA TODAY: 8 September 2004):
In the calculus of Internet crime, two of the most sought-after commodities are zombie PCs and valid e-mail addresses.
One indication of the going rate for zombie PCs comes from a June 11 posting on SpecialHam.com, an electronic forum for spammers. The asking price for use of a network of 20,000 zombie PCs: $2,000 to $3,000. …
To put a zombie network to work, an attacker needs a list of targets in the form of e-mail addresses. Lists can be purchased from specialists who “harvest” anything that looks like an e-mail address from Web sites, news groups, chat rooms and subscriber lists. Compiled on CDs, such lists cost as little as $5 per million e-mail addresses. But you get what you pay for: Many CD entries tend to be either obsolete or “spam traps”  addresses seeded across the Internet by spam-filtering companies to identify, and block, spammers.
Valid e-mail addresses command a steep price. In June, authorities arrested a 24-year-old America Online engineer, Jason Smathers, and charged him with stealing 92 million AOL customer screen names and selling them to a spammer for $100,000.