I'm in the $75/month level for them. Most of the services -- aWeber, MailChimp, Constant Contact -- are ~$70/mo for >5k subscribers.

If that's exactly what you need, that is.

Also, most businesses start making money off their lists -- or trying to -- a lot sooner than I have. I spent the first year thinking that the blogging was supporting and promoting the book. Now that I realize there's more money in a responsive list, it's already pretty big and unwieldy.