I am taking Frugalwoods Christmas card advice for my birth announcements. I'm printing postcards, not "birth announcements" on vistaprint (cheap; $7.49 for 50- and yes, I really do need that many; my family is huge) and mailing them using a postcard stamp (way cheaper, especially with the rate hike). To my mother, MIL, and grandmother in law I will put the card into an envelope to protect the photo.
But mainly, for my family, it is a social norm. People would be insulted if they did not get a birth announcement.
90% of people throw them away after thinking "cute baby", but if they don't get it- major uproar. But some people keep them on the fridge for years.
But it will cost us under $30 for the whole shebang and keep the family happy. No one lives near us, so very few people will actually see the baby as an infant.