I don't think I'm reading this incorrectly, but it seems that a religious organization, whether or not it is incorporated (a state I wouldn't recommend) or has an affirmative IRS 503(c)(3) ruling (that's a recognition as a public charity by the federal tax authority, for my overseas readers) is eligible to apply for a nonprofit mailing permit. This permit could make mailings quite cheap.
From the USPS (postal service) Domestic Mail Manual section 703
A religious organization is a nonprofit organization whose primary purpose is to:
a. Conduct religious worship (e.g., churches, synagogues, temples, or mosques);
b. Support the religious activities of nonprofit organizations whose primary purpose is to conduct religious worship; or
c. Further the teaching of particular religious faiths or tenets, including religious instruction and the dissemination of religious information.
This could be quite an advantage to a small church trying to make an outreach through direct mail, or a ministry that makes mailing its main activity, and is small enough to not warrant formal recognition.
Does anyone know if this is actually the case?