Direct Mail.

One of the most cost-effective ways to establish and expand
a strong customer base is through direct mail campaigns.
It has also been shown to help get new customers, increase
customer loyalty and drive sales. Direct mail can be used
to send your customers invitations to special events created
just for them. Even though the sender can expect only a one
to two percent response, the comparably small cost involved makes it
a feasible alternative to the traditional approach to advertising.