Organic Blog Growth?

I'm sure there are a few successful site owners on here who have seen their subscribers grow organically after a certain point, without the need for promotion. I made the estimate that if I got 100 subscribers my site would probably grow from social networking and voluntary back links from that point on. Does that sound like a realistic estimate? So far it has only cost about 20 bucks to get about 50 subscribers, so I wouldn't mind taking the promotion a little further if need be.

Akmacca, you can set up a campaign with Google Adwords or Yahoo Search Marketing where you pay by the click for people to arrive at your site. Or you can use Bing too, I think. Just remember, people are looking for solutions--that is the main reason one might subscribe to something. Entertainment is a possible too, but harder to maintain visitors I imagine.