If you are requesting information be returned to you in your mailing, Business Reply Mail might be the way to go.  With Business Reply Mail you only pay for the pieces that are returned to you.  It can be less expensive than including a self-addressed envelope with a stamp depending on your expected return rate.

Appropriate uses for this form include:
Responding to event invitations, submitting payments, updating contact information, completing membership or registration forms, requesting services, or providing feedback.

Business Reply Mail Artwork Request Form