The most direct way in which spam can cost consumers money applies if you're paying for Internet access by the hour. In that case, you're being billed for the time that it takes you to retrieve the message and read it. Spam can also cost consumers money indirectly. Spam takes up bandwidth space and increases the amount of mail that goes through a given Internet provider's e-mail system. Internet providers have to constantly upgrade equipment to be able to support the traffic and data that goes across their systems.
Providers sometimes pass upgrading fees on to the consumers through higher rates.
Using this line of reasoning, spam opponents point out that such upgrade fees could be mandated by the large number of junk e-mail messages going across the system.