I've got 4,200 people on the paid newsletter at £6/month. It works. It's also the only thing I do, and delivery takes basically every hour I have.
Everyone keeps telling me to bolt a course on top — one-off revenue, higher ticket — but I've watched two people I know do that and end up with a course nobody finishes and a newsletter that's gone quiet.
So: do I keep the subscription as the whole business and just charge more, or split the hours and add a product? If you've done either, I'd rather hear what it cost you than what you'd recommend.