Yikes, good question. Our main concern is that the Show HN thing should present something you've made that exists and works—that it be more than vaporware, a fundraiser or a landing page. I don't think that implies that it has to be free.

That said, users guard the Show HN "brand" pretty zealously. If I'm making the wrong call here, I expect they'll tell us by flagging posts that they think use "Show HN" incorrectly.