The final price will depend on what you decide to do, whether it's a neighborhood mailing, a database mailing or an email newsletter to your database.
The more you mail, the cheaper it is per unit. You will be surprised how cheap it is to mail to many homes at the same time.
At the end of the day, it's about Return on Investment: Do you think the marketing investment will return sufficient closed listings to make it worth your while? For agents sending newsletters consistently, it tends to be a worthwhile investment.