For a static site, I think 100 submissions/month for free is probably more than enough for the majority of people. Though going straight to $19/month is a pretty big step if you're just hosting your own personal website/blog.

It's $0,019 per submission, which I think is a fair price if you're actually sending that amount (and making money from it). It would costs you much more to build unless. That said, for personal (free) use there are a lot of alternative options.